The cat 22 mk ii is a little beamier, has a standard 'pop-top' at the companion way (handy for camping/anchoring/adding spaciness in the cabin), has a gin-pole mast raising system, and comes standard with a centerboard. Basically, they took the best options of the cat 22 mk i, and made them standard.
If you are going to leave the boat in the water for the most part, splurge and go for a mac 26-something. I'd reccomend the D, as I've raced on the x, s, d, and m, and the d is probably the best racer. The s is also good, but I think they made more d's, and so you can probably find a better deal on one. I wouldn't pay much more than 3 grand for one, maybe 4 grand. Gotta love the modern economy.