If you can afford it, the 74GB Raptor appears to be faster than the 36GB, because of Native Command Queueing and lots of other things about which I'm no expert.

I'm putting a machine together for functions that will include media editing, and I'm finding that most people recommend having multiple drive subsystems for that kind of work, instead of a big RAID 0 volume. That's because editing/encoding programs dealing with large files will often read from a source location and write to another large file; if the two big files are on the same logical drive, even if it's on a RAID 0 drive array, it causes the whole thing to thrash. I'm just pointing out that sometimes, having your drives separate can actually be better. The 74GB Raptor is apparently screaming fast; it's what I've picked for my system drive.