Worth upgrading a Fenn Elite for flatwater marathon?

Interested in opinions on upgrading from a  Fenn Elite for flatwater marathon.

I am 210lbs /95kgs and been paddling an old carbon Elite on the flat for the past year, more comfortable and faster on that than my epoxy  gen 1 v10 sport. I have padded up the seat slightly to improve paddling position. 

I am an intermediate who is paddling about 11kph currently. Is there a significant difference in speed of the more modern designs in the flat? 

Cheers,

Toby

'flatwater marathon' could mean almost anything. I compete in so-called flatwater marathon racing; they are actually 12.8-21km races, held on rivers and canals.
I doubt you mean the same sort of races, partly because a ski would absolutely suck at those races (poor turning, terrible for portages). 
Could you give a bit more information about the race?

Similar...12-20km, on lakes and enclosed waters. Most people in quicker divisions are using k1's. We don't tend to portage in the divisions I paddle.  Paddling a k1 over a marathon is slower for me due to stability, I find an elite ski is the quickest. Cheers

If you can paddle a ski in waves, you should be able to handle a K1 in a race. Pick the right K1 though! The stability varies a lot (from bathtub-8s to stab 1s).
The boat hull profile has a huge effect on the stability in use. My club has some beginner boats (stab 6) that I find horrible in wash. The boats get their stability from a square mid-section and that means they tip unpredictably in a boat wash. 
My own K1, an old delta-style, is a very skinny stab1, but isn't affected much by boat wash, waves. Just feels very unstable when you first get in. Doesn't change much when you hit boat wash. 
What difference does changing a boat make?
Well, going from a stab6 boat to a stab 4 boat, if you can paddle both well, will make you about 1 min faster over 10km. 
I think you are likely to get improvements in your racing from technique improvement and that will require you to tackle paddling a K1. They'll turn faster (I've lost races at the buoys), sprint start faster (getting on the lead group is the best way to get a podium finish).
If I brought a K1 in an ocean race, I could make it round the course. Maybe. I'd be better off learning how to handle a ski. Horses for courses. 

There is a slight improvement in speed in different boats. The old elites have a fair bit of rocker which made them good on waves, relatively stable and slightly slower on the flat.

You don't necessarily need a newer boat to go faster on the flat, because the trend at the moment is to give everything more rocker. Some of the older boats will be faster.  Any of the low rocker boats made from carbon should be faster. Uno max, gen 1 V12, Carbonology Flash, Fenn Glide or a carbon Red 7 pro (my favourite). Any of these boats in carbon will be faster. 

Put on a small rudder. This makes a huge difference in speed. The downside is it also makes wash riding more difficult. It also make turning a challenge. 

I am sure there are other low rocker boats out there, but its early and I need to go for a paddle

Interesting article here by Greg Barton on flat water speed comparisons
Epic  Ski -k1 speed comparison 
This supports the theory that the fastest is what you are most stable in. ie a k1 is only faster IF you are a gun in a K1. Interestingly he believes even on flatwater an intermediate paddler doesnt get much improvement on an elite ski compared to an intermediate ski. Especially over longer distances as you can't consistently sustain it. That said I think if you are racing flatwater there is probably more room to develop  in a K1 as it is more paddler limitation than boat limitation. Much less effort manhandling a K1 compared to a V14 too.

I think being 95kg, similar to me, a longer ski is probably easier than a lower volume k1 even assuming the K1 is rated for your weight.

I currently paddle 50/50 on v10sport and a stab 3 K1, and they are roughly the same time on flatwater over distance, ski is way more stable, but k1 is still a fairly new style of boat for me so room to improve and will be moving up to stab 2 shortly. K1 just feels better/faster even if the clock doesnt say so, just more rewarding

Thanks folks, it is a really interesting topic! I have a v10 sport, a stability 2/3 k1, as well as the Elite. I am definitely fastest in the Elite in the flat, partly down to the boat for just fitting me well. I also have read that at 95kgs I am maybe slightly heavy for a k1. I am about 0.5kph slower in the k1 it is more technical to paddle and maybe 0.2 Kph slower in the v10 sport. It's 2kgs heavier as the chop increases the difference disappears. Might try a lower rocker ski and see what the difference is like. Cheers 

I know when I got my K1 I had to match the boat to my weight, and got a high volume model to suit -  www.kirtonkayaks.co.uk/home/our-boats/k1/3-typhoon  

Is your K1 designed for the weight, or could you try one that it? 

It is hard to resist the allure of a new ski once you have begun to lust after it. I have given in many times. 

Let me throw a little ice on things. With 11kph race speed you are an intermediate paddler like most of us. As bartons numbers demonstrate, speed gains between boat classes are not huge at intermediate speeds. This is because of the trade off with stability of course, but also has to do with the relative contribution of friction vs wave generation to boat drag at different speeds. At any rate if there is not a huge difference between boat classes at intermediate speeds then there is probably almost no difference in speed within boat classes at your speed. i suspect that any slight difference in hull speed between the various elite hulls would be dwarfed by the differences you will find in comfort and ergonomics between the various  skis. So if you are going to trade to a different ski, make sure that it feels more comfortable and more powerful to paddle than your old ski, otherwise It is probably not worth it. 

Probably the right answer is to take the money you would have spent on a new ski and spend it on coaching and training. That will get you more speed than a slightly different hull i think. Mind you I have never made that wise decision and hired proper training myself, but it is probably the right thing to do. 

I think coaching is the game changer for flat water racing as it is all about consistent technique much of which is impossible to self analyse. The stability of a ski over K1 can actually mask this. Being coached in a K1, even if you end racing a ski on flat water is extremely beneficial. Of course open water is a different game altogether where technical repetition is not so important.