Ok, so I'll start my carefully considered, logically irresistible, verbose and somewhat wine-fueled response by congratulating myself with a successful revival of this here most popular thread in the history of the forum (Rob feel free to correct me on that). Well done, me!
And now to answer the points of the discussion: Impala is absolutely correct in saying that my main point is that good boat contact, IMHO, overcompensates for the inherent instability of an elite hull. Obviously up to a point. In my case this point was between an Elite S, and Glide. The narrowness of the bucket of the Elite serves my need well enough; any narrower bucket starts impeding the rotation. And, of course, paddling the Glide in messy chop is, very taxing on ones mental concentration, it demands constant attention, the moment you take your eyes off the sea it wants to shed you (or at least me, rather). Whereas Elite not only allows for incredibly predictable roll (the roll of the Glide is pretty predictable as well, it just starts sooner and is shorter before you find yourself swimming), it also allows you a big enough margin before the roll is induced, so you can space out when doing the upwind chore, and you'll be fine. Probably has something to do with a C shaped oval hull of the entire Fenn lineup, with no edges that make for a point of no return once you roll past them..
As far as padding the seat with foam – I guess I'd rather buy a ski with a bucket that fits me already, I don't think it's too much to ask.. I've been pretty lucky so far in that regard; for instance, I'm aware of the "Fenn dead leg" phenomenon that some people experience, I'm just thankfully not one of them. Btw, I'm not associated with any manufacturer, and my exposure to skis is limited to all the Fenns, V8, V10sport (hope to try V12 in near future), Think Eze, Nelo 510 and 560.
Boyan, on the other hand, seems to agree with the one sided statement that a well fitting, as snug as possible ski is better than a loose one, so that's squared away then. Especially if he admits that the inner fit of the bucket can trump the outer stability of the hull. I know a two sided argument when I see one as well!
Now, I'm going to push back on your push back.
Firstly, let me assert that the stability of a given paddler on a given hull was kind of taken for granted by me. Obviously, one needs to feel relative comfort on board the vessel one paddles, that goes without saying. The relativity of that statement could be discussed, but let's say for the sake of an argument that you're mature enough to assess the sea conditions correctly, and while paddling your fastest, with rotation unrestricted by safety considerations, you manage to fall in once every 1000 hours on a given boat. And yet you have enough wonderlust to go in the highest possible (safety-wise) seas all the time, resulting in that 1/1000 capsize. So, the stability factor you mentioned, is not really a factor, because for such a paddler stability is a function of concentration at worst, and is a given, at best.
Secondly, having put stability outside the pole of the discussion, let me do the same (almost) with speed. I'll grant you the numbers you cited regarding the top speed of the boats in question, making the advantage of one over the other truly negligible over a puny 40m distance. I, being a lazy, non-foam-padding luddite (I don't even own a smartphone, or a TV, never have, and this is my third ever "post" on the Internet), am absolutely content with those numbers, since all speed measuring gadgetry is way beyond me. They sound about right. However, I was not talking about the top speed but rather about the acceleration. Now, you will recall that my swap from Swordfish to Elite S was also accompanied by what feels like a significant weight shedding (on the part of the boat, not me, alas), which has to contribute to the acceleration as well.
Now, as I'm sure you know only too well, there comes a point where the ability to accelerate faster would determine whether you are able or not able to catch a wave, especially from a dead start, especially a fast non-wind-generated swell. At that point the marginal top speed difference transforms into an absolute dual-proposition difference between riding a wave more or less safely and controllably between the rocks, and being picked up by a breaking wave and praying it won't deposit you onto the rocks. I may have exaggerated for clarity sake, but come a big enough day and suddenly my exaggeration becomes an understatement..
Lastly, I'd like to stress again, I'm not arguing against the loss of stability scenario. Everything Boyan writes about that is gospel truth. If one cannot paddle ones best (full rotation) without swimming, one is in a wrong boat or a wrong sea (which can happen due to the aforementioned wonderlust and overestimation of ones abilities; I have one especially dear memory of finding myself at the bottom of a conical whirlwind, where every time I raised a paddle it was tugged in a semi-circular motion, because the wind would change direction 3 times a second; had to wait it out for 30 glorious minutes outside the boat).
I'm just saying that Surfski 600 concept shouldn't be reserved for beginners only (unless Boyan, its creator, says different - got to respect the copyright) , and if ones abilities change, so should ones Surfski 600. Arguably it should become longer. Or the sea should become higher. Or both.
Which brings me to some downwinding questions for Boyan. You are an accomplished paddler and extremely accomplished downwinder with no stability issues whatsoever. Why do you paddle a V8 and not a V12 or some such? When on your own I mean, when not teaching anybody? Are the runners intervals so small in Tarifa (they don't look to be) that anything longer than a V8 wouldn't fit between them? Or do you prefer a slightly slower boat so it won't outrun the wave you're riding? But then aren't you making it much harder for yourself to plough through the hump of the wave in front of you (I know you prefer to outmaneuver it on its shoulder rather than plough through, but surely sometimes you have to)? Or is it only due to the ability to turn the shorter boat quicker?
Ok, actually at this point I almost convinced myself that in Boyans ideal sea conditions it might make more sense to go for the shorter boat... However, in a faster boat you wouldn't need to do as many weight shifts back and forth, and by zigzaging even more than you currently do you can make it fit between the short intervals (if that is indeed the problem); it also makes the distance you travel bigger so you don't outrun the wave?