Have you seen this discussion on adobe forum? It is the grandaddy of all Premiere Pro disk discussion, and has been pretty heated for a couple of years:
http://forums.adobe.com/thread/662972?start=0&tstart=0
What it boils down to is this: get FOUR 7200 rpm disks and set them up as follows:
C: OS, Programs
D: PageFile and Premiere Pro Media Cache
E: Previews and Exports
F: Media and Projects
C: can also be SSD, but that will not really speed up PP per se. If you do that, you might also put the PageFile on C:.
IMHO, you should not use RAID of any type unless you meet all three of these conditions:
(1) you are editing uncompressed video (only a few pros really do this), or multiple complicated compressed streams (which is pretty advanced);
(2) you have a lot of funds;
(3) you have a lot of time to dedicate, or a tech support person; and
(4) you've already maxed out your processor (i.e. hex-core), RAM (16 GB and up) and PP-supported GPU.
If you want RAID, you should keep your OS, program files and page file away from the RAID (unless you've got a 6+ disk RAID, which you really really should not do unless you meet the above conditions).
Don't forget that you still have to back up a RAID, regardless of whether it's 0, 1, 5, 10 or anything else. RAID 0 is downright dangerous.
Hope this helps.
EDIT: fyi, I have the three-disk version suggested in that adobe forum thread, and it works great. I will upgrade to 4 disks in the future.