you dont need identical drives it will just split it to the smallest and slowest.
ex. if you have a 50 and a 70 you get 100 when together in raid 0.
as far as your other comment. Raid 0 is Stripe Set, never heard it called speed raid but it could be. i know when in raid PROFORMANCE is increased, not read/write times. read/write stay the same but because data is half the size it gets done quicker.
As far as throwing together 2 320 gigs, maybe im just to "old school" for you guys lol, even tho im not that old actually i just take more of an old school approach to things lol.