One serious deficieny with that system in using a SCSI raid array; bandwidth ! That why I wen from a Athlon3000+ and a K8v to a Tyan Thunder dual Opteron board, not for the dual cpu's (even though I have alwways wanted a dually), but for a 64bit PCI-X 133 mhz slot ! My transfers went from 60k to 195k on the same card and SCSI drives ! I love SCSI, but if you don't do it right, you are wasting your money. I hate to say it, but with your budget, a single 15k MAS SCSI drive is about all you could fit in your budget. They will leave the Raptor in the dust, and but you will pay ! $519 for the 73 gig MAS drive, and you will need a controller. You can get a decent U160 controller (your stuck to 133 mps bandwith anyway) for $32.
And to the comment that for a single user, its bragging rights, NO, it does make a difference. A single 15k 3.6 ms access Fujitsu MAS drive will murder a Raptor. However, a 6800GT and 1-2 gig of memory will suit a gamer much better. If both fit in the budget, great, otherwise I agree that the 6800GT is probablt a better use for the money.
And one more plus for SCSI, they live almost forever, and have a 5 year warranty.