If you happen to have a SCSI Kit I'd recommend you'd go for some SCSI drives since you will get better results when it comes to speed. Also, as far as I know the DMA on the Mediator is a bit funky, since it uses the GFX-card (or the network card, not sure) to enable DMA (long time ago since I discussed this very issue with someone that knew exactly how it worked). Anyhow, my point is, the DMA-handling will also be better with SCSI.
If someone knows this better than me, please correct me, because like I said, I'm not really remembering exactly how this actually is working.