Clothing for wet, mild and windy

'mild' = air temperatures of about 4-8C (39-46F). Water temperature about 4C in winter, occasionally dropping below 0C in shallow bays.
'wet' = drizzle or very heavy rain (the sort that hurts)
'windy' = a 'quiet' day is under 20knots, gusting to 30knots. A windy day is 40 gusting 60knots.

Surfski paddlers have a unique set of problems compared to kayakers. Exposed legs and feet hugely increases the exposed surface area. On the other hand, the effort levels are commonly higher, in theory generating more heat.

What are the clothing options?

Drysuit
The gold standard must be the breathable dry suit. It doesn't restrict movement, sweat is slower to build up. Evaporative cooling is reduced. The downside is the cost. I haven't paddled in a drysuit.

Full wetsuit
Wetsuits are far more restrictive and don't offer the same insulation values. That said, if you are paddling in rough conditions, get slapped by waves, fall in; a wetsuit offers a lot of protection. My personal gripe with them is twofold: a full wetsuit is very restrictive on shoulders, making paddling hard, and unless loose, they make it difficult to sit in the surfski position. If tight, a wetsuit is actively pulling back when you are in the seated position.
A sleeveless design addresses the restriction on arm movement, but doesn't solve the issues with sitting.

Wetsuit trousers + base layers and cag
These solve some of the problems with exposed legs (although I've found it necessary to wear thermals under the trousers for insulation). Surfski is a wet sport, you are often sitting in some water, so insulating your bum and legs is important.
Cags vary in quality. Mine is very cheap and frankly rubbish. The best that can be said for it is that it cuts down windchill. Better quality cags will keep your upper half dry from splashes.
This combination is versatile, in that the insulation worn under the cag can be varied according to the weather - or even changing conditions (the same applies to the drysuit).
The serious negative is that if you take a swim, you are going to get a load of chilly water dumped against some bits. If wearing the right gear, it won't be a soaking (I once swam across an icy river in a t-shirt, wool sweater and goretex jacket - when I got home, the t-shirt was mostly dry).
    
Price-wise, for many of us the best option is going to be the combination; Wetsuit trousers + base layers and cag. If we do walking, running, then we probably already own the base layers and insulating garments for the top. Wetsuit trousers are cheap. 

If you own a wetsuit and want to have a session practising remounts if rough conditions, I think they are the best option. 

What are the thoughts on my analysis?

We got similar winter temperatures here. Although last week was unusually cold with night temperatures down to -15 Celsius. Right now I am waiting that the ice will thaw. My choice for winter paddling is a breathable Thyphoon Drysuit with attached latex socks even though the water is very calm here compared to your situation. But with water temperatures around 0 Celsius I won´t take any chances. Underneath I wear functional wool underwear and as a middle layer a thin stretch-fleece-suit from Palm. As long as the air temp. is below 10 C it´s O.K and I will not overheat. Of course my under garment will be wet from sweat after a training session but I don´t mind that. When the temperatures are rising in spring I change to a Long John Wetsuit from Langer. In my experience the wetsuits that are made specifically for (whitewater) kayaking are not so restrictive in a sitting position. Overneath I either wear a very thin (0,5 mm ?) Neopren-Shirt or a so called Aquashell-Shirt which is waterproof and has Fleece inner lining. This setup is also my choice for open water paddling in late spring or early summer when the water temp.here is still quite low. 

You guys are hard core. Or maybe just warm blooded!

When I lived in Connecticut and Massachusetts would wear light neoprene shorts or pants and a neoprene t-shirt down to about 55* in my stellar SR, but it was so stable there was almost zero risk of falling out and the reservoir was small enough no waves would come in the cockpit.

Once it got below 50* air temp it was a little more tricky and depended on the water temp. In the fall when the water was still warm I'd stick to the thin neoprene combo and maybe a windshirt. In the spring when the water was freezing, I was in a drysuit until May regardless of outside temp. I would just wait for cooler days so overheating wasnt brutal. Also we got a lot of cloudy days which helps a ton in a drysuit

Now on the pacific, I have a 3/2mm full suit and a 1.5mm Short sleeve (full legs). I use the 3/2 all year except for summer. Our water is about 50* in the depths of winter and 65* in september. Havent used the drysuit since coming to california, but I cant bring myself to sell it either. I have a high end Oneill surf suit and dont find it restrictive or 'hunching'. The 1.5mm is so thin its not noticeable while paddling.

Personally, for any weather less than 46* as you originally propose, I'm headed towards a drysuit. Especially true as you approach freezing. Freezing = drysuit

I paddle in the PNW, and we're in similar cold water high-wind environment. Below is a guide that I came up with for choosing which clothing to wear, based on what the wind is doing, as well as air temps. It's predicated on very low swim probability and high intensity paddling, so if you are a new paddler or an intermediate making the transition to going out in the big stuff, this might not be the right guide for you. 

Above 50º / High Wind (20mph +) Thick thermal paddling tights / compression shirt, no gloves or socks. 

Above 50º / Light Wind (20mph max) Thin thermal paddling tights, or shorts and a compression shirt, no gloves or socks.

Below 50º / High Wind 1.5mm Hydroskin or similar pants and top, compression shirt, .5mm gloves and 1mm socks

Below 50º / Light Wind 0.5mm Hydroskin or similar pants and top, compression shirt, no gloves and 1mm socks

Above 43º / High Wind 1.5mm Hydroskin or similar pants and top, compression shirt, 1mm gloves and 2mm socks

Above 43º / Light Wind Thermal tights and a compression shirt, .5 hydroskin gloves and 2mm socks.

Below 43º / High Wind 3mm Farmer John or equivalent, 2mm gloves and 3mm socks.

Below 43º / Low Wind 1.5mm Hydroskin or similar pants and top, compression shirt,1mm gloves and 2mm socks

Below 33º / High Wind I don't paddle (we only have a handful days this cold, but the risks are very high).

Below 33º / Low Wind Hybrid drysuit, 3mm gloves and socks.

I run separate dry pants and dry top in such temps.  I like the flexibility this affords in early springtime when daily temps can vary dramatically.  When it warms up a bit I shed the dry top but keep the pants on.  When temps go higher I then shed the dry pants for neoprene tights.  Along the way accessories like gloves, pogies, hats and booties are shed with the end goal to be naked by the month of June.

I understand the security/safety of a full suit but am willing to sacrifice a bit for the flexibility.  I am on a very stable boat and not on open water.  Overheating has never been an issue but then again, I don't work really hard at it in winter.  For me it is a time of low HR paddling.  Intervals sessions while wearing that many layers is not fun.  The limiting factor for me is cold feet.  Despite 5mm WP boots and wool socks underneath, my feet get very uncomfortable paddling longer than an hour in temps from 0-5.

I seem to run colder than most people.  I'm always amazed to see my friends in minimal clothing/no gloves/no hat while I am shivering under pounds of neoprene.

Interesting and relevant topic for me. I paddle year round on the Chesapeake Bay in Maryland. Right now water temps are in the mid 30's (F). I've been experimenting the last couple of seasons with the right combo for cold winter paddling. It's hard to balance comfort/safety. I try not to go out in winds over 20 knots in the winter, but that's not always possible. Yesterday it was predicted to blow about 5-10, with gusts 15-20. I was wearing  a NRS 3mm farmer john with a Mocke 2mm paddle shirt over top and 7mm boots. I was sweating during a relaxed to moderate paced paddle in my Epic v10. It was cold enough that the deck of my ski and shaft of my paddle were icing up pretty good. The 7mm boots are a new addition. While warm enough for below freezing temps the size 13 and thick neoprene makes it really tough to stuff into the small foot box on the Epic skis. When I first tried a drysuit it was too restricting  with the latex neck and way too hot. I prefer a wetsuit even though it might not be as flexible. 

Wearing a neoprene shirt UNDER a Farmer Jane/John allows decent freedom of movement while still keeping the armpits, torso, and neck well-shielded from cold warmer if dumped.

I have not bought one yet, but adding a neoprene front-zip jacket over the above would be an easily-shed layer for days when the sun is going in and out of the clouds. 

Mr charley if I am paddling in flatwater in those conditions i wear thin neoprene pants (trousers in britain), a thin baselayer top and some sort of wind shell (cag). If I am downwind in waves in those conditions then I use a full wetsuit, either 2mm or 3-4mm depending on the conditions and danger level. My 2mm full suit does not impede my stroke at all. It is a higher quality “super stretch”
model that cost about $250. It is tight enough that after a brief swim some parts of the inside sometimes remain dry. My 3-4mm suit is made of cheaper neoprene. I do notice it restricting movement a little bit for the first few minutes, but once I am pointing downwind I never notice it. My hands get cold easily so below about 50F i always have pogies or gloves or mitts. Flatwater I use pogies. Downwind i choose gloves or mitts. If you end up stuck in frigid water and you chose pogies instead of gloves or mitts than you only have about 5 minutes before your hands are too weak to do a remount, grab a rope, etc. I think choice of hand protection is an under-appreciated safety issue in cold water. All of that said, it’s hard to specify how much clothes someone else needs because it depends on how thick their body is as well as how hard they are going. 

I nearly always use pogies - and in the Hebridean winds, they have a secondary benefit of reducing the chances of the wind snatching the paddle from my hands.

Second paddle here yesterday; much warmer (about 8C, erm 45F?). Stronger winds though, blowing 20knots gusting to high 30s to start with. Got stronger later and I decided to head in.

This time I wore neoprene trousers (cheap ones, I think they are 3mm). Icebreaker merino on top with an old Montane fleece and pertex jacket. 

Great combination. The jacket is designed for climbers and doesn't inhibit movement at all. Blocks wind, water just drains through. 
The only place I felt any cold water was at top of the neoprene trousers, when a wave slapped over the boat and filled the cockpit (it was wind against tide, short choppy and steep).

Unfortunately there is no way to dress that will be both comfortable while paddling as well as sufficient to keep you warm if you end up immersed in water. Sometimes when it is super cold I actually like it to be raining and blowing as well because it makes it easier to wear more neoprene. But it is a tricky problem without a perfect solution. Make sure your remount is rock solid and practice it in waves too. 

I haven't practiced remount in waves yet.
Really must, but I've been reluctant, for two reasons:
One - the wind is currently very strong. I'd have little time before being blown onto rocks (was thinking how calm it was this morning when I went jogging; it is only blow 15 - 25 knots).
Two - this is a fishing community with lots of cottages overlooking the loch. I'd hate for someone to get alarmed and come racing out into the loch to 'rescue' the paddler who keeps falling in.

Next weekend the forecast is for just a force 4, so I'll spend more time on technique and pick a good spot for remount practice.