From what I understand, SATA isn't much of an improvement over 80 wire IDE. 4 drives in RAID 0 is asking for a system failure, in my opinion. (one drive goes down, they all do)
If I were you, I would probably get a couple raptors + a new PCI card, and then run those and the other 60GB drives.
I'm not sure what you need all this speed for, but if you have 2 RAIDed drives, you should be able to put your OS/applicaition on one and your swapfile/temporary file on the other.