I'm going to chime in here and wonder if this fastination with all out speed is somewhat out of place with reference to paddling. Yes indeed it is nice to have a fast kayak, but if speed is your real interest, then I have to also wonder how paddling is going to satisfy that lust in the long run.
Let's get honest, guys, there isn't really that much difference between a super fast kayak and a so-so kayak. What?--Maybe one point something mph? If competition is your thing, then go for it, but for just enjoyable paddling, I want a boat that cruises with ease and is comfortable and dry in the rough stuff and won't put me upside down if I get sloppy. Oh, and the boat has to look good.
You make some good points and I agree with a lot of what you are saying but it doesn't infer that any variation is wrong. I'd say a top sea Kayak would have a normal kayak beat by a couple of knots or more and also have the ability to sustain top speeds for much longer. When travelling 16miles or more, you'd like every advantage. The casual paddling speeds would hence be compromised along with handling or stability per se. Though there are fantastic kayaks which will cut through waves better than some of the more traditional boats. Watch the Epic videos on youtube.
I haven't used any of the "fast" boats so I can't yet form an opinion about if they work for me or not, though I think I will be pleased to an extent. Currently, my 16.7 boat will not go much faster than 5.6-6mph seemingly as I've tried to paddle it very hard.
Oh, and I prefer skeg.. :-)