Dito.

SCSI will slightly reduce the load times but it won't make any real difference to WoW. When I built my current system I was debating using SCSI II drives, but then downgraded and planned to use Raptor drives but then downgraded to SATA2. If you're after a fast kick ass machine for other games, or apps that are HDD read / write intensive then SCSI has no place in a home PC. If you have dollars burning a huge hole in your pocket and want to spend money on anything / everything then I'd go ahead.