If you want a lot of speed, I'd either go SCSI, or get a SIIG ATA 133 raid card, and run 2 drives as a striped RAID, which you initialize often (after each project).
Two WD Jumbo Cache drives will run close to 100MB/sec both ways on a striped RAID setup, which should be fast enough. If you have the $$$, 8 Seagate Cheetahs on an ATTO Dual Channel U320 card is the way to go (215MB/sec, sustained, both ways).
Then add a drive if necessary for your apps/storage.
The key to speed is only using the RAID for work (not storage), that way you can wipe it often, and always get great captures.
If you don't want to do that, make a partition on the RAID which has enough room for eveything you wanna do.
