For the OS/Apps/Games, there's the Raptor in it's class and there's the rest ... trailing behind in the next slower class. Since most people don't change HDs as often as other parts of their rig, I'd go with one.
If you don't happen to run a server, RAID 0 won't give you that much of a benefit, unless you boot up Windows XP very often, which does profit from RAID 0, when optimized.
For your data, the money is better spend with a bigger and slower drive (as Bar81 pointed out)
Don't even think about SCSI, its optimized for servers and will be slower in a desktop than a Raptor while costing a lot more.