2x vertex2 in raid 0 should be faster performing then a non-raid0 solution. most ssds cannot tap out sata2 so i doubt that most average drives can fully take advantage of sata3. i dont know the individual specs but you can easily find them online (perhaps even on toms).
the thing with raid 0 is that if one hard drive fails... you are completely screwed. you gain speed but that is it. regular backups are highly suggested. if you want the fastest performing system you can, raid0 is the way to go.
if you have individual drives you still only have 1 drive running the os and one drive for storage. if either one fails you're still screwed but at least your programs or your windows install would survive. backups are still highly suggested. you can save backups to your other drive and not be screwed if you get a failure.
raid1 has the same performance level of one drive but essentially does the same thing as backing up your data every single time you make a write. the downside is that if you have two drives, you only have the space of one drive. the upside is that if there is a failure you can just keep chugging along and just add in a new drive to replace a failed one without losing any sleep.