My Etap21i used to 'fly' and was also unsinkable (Cat B as well)... a great boat.
I should of added that your three criteria of capable, seaworthy and speediest are somewhat mutually exclusive... for speed then go for a mini-transat 6.50 (the POGO 2 for instance)
I sail a beneteau first 211 and they're pretty nippy although I am not sure I'd fancy it in much more than a force 6. It is "unsinkable" too (now there's a challenge) and RCD B if that gives you any comfort. However one of the forumites on the jester forum suggested it was just the yacht for the challenge so it takes all sorts.
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Hurley 22 - tremendous blue water record and a very capable performer under sail, very fast for her waterline length.
Based only on knowledge of boats I have sailed in I would add the Pandora and the Corribee to the list (you didn't mention headroom in your list of important factors!).
If you'd have said 26', I'd have said the Contessa 26.
Oh yes, as Webcraft says, the Hurley as well - the 22 also looks just like a sailing yacht should look.
It seems to me there is a huge difference in the nature, weight and cost of 20ft to a 24 ft boat. Within that range you can get a very light 24ft or a very heavy 20ft. The heavier boat will deal with heavy seas especially on the nose while a light boat will show a real turn of speed in calm water and especially in light winds.
I race in a fleet of about 10 keel boats in the range you mention and even bigger. None would be known to Britishers. Though the designs would seem vaguely familiar. Mine sits at the bottom extreme of light 950Kg with lifting keel 21ft but has just won again the prize for most fastest times over some 25 races for the season. However the boats I can beat are far more comfortable and powerful in rough water. They tip the scales up to 3 times my weight so have a far better motion. Some of course also have the separate toilet compartment inboard engine and far more room. (and cost)
I think you need to do some crewing on various boat to get a feel for the difference. I love my little boat (after 27 years) but often wonder if my sailing style (preferences) have been dictated by the boat style or whether my sailing preferences are best suited by the boat I have. I guess i am too old to change and try something heavier though I often dream.
To find what suits you will often take many changes of boat (expensive) so choose slowly and carefully. good luck olewill
The old Seawych is a good example at the bottom of the scale, very seaworthy and more comfrtable thanit.e size would make you think, at the upper end the Maxi 77 is also a good sea boat and has almost 6 foot headroom just below the hatch.
Basically there are a lot of good boats in the range, you really need to look at some to get a feal for what suits you.
Hijacking this thread for a second.
If/when I move from a dinghy up to a cabin cruiser, are there any booats out there in the sub-24ft category that have
a) standing headroom for midgets (me and herself both under 5'6 tall)
b) sufficient seaworthiness to cope with trips around the Hebrides
c) light enough to be towed on a post-'97 license (so, about 1250kg or less)