You are pretty much right about everything -- except that you also have to factor in the size and power of the engine, i.e.,the relative amount of sail area, the sail plan (main only or main and jib), height of the mast, etc.

Compare the A-Class cats, which are 18 feet long and now weigh 165 lbs or something anorexic like that (I can never remember exactly), and the Hobie 18, which weighs 450 lbs. (according to the company specs). The A-Class has 150 square feet of sail in main only, and the Hobie 18 has 220 square feet of sail in main and jib. The Hobie 18, at the same length as the A-Class, is obviously a much more forgiving boat. It is not just because it is heavier but because it has a smaller engine relative to the boat's weight.

They are all fast and fun. Some have a wider range of wind speed and wave conditions they (and you) can handle comfortably.