If I were to choose, I'd Go for IDE. IDE controllers and hard drives are more cost effective than those of SCSI.

As well, I would second to what lordsmurf said if you don't use SOS (server operating system) it ain't make a huge difference. Only server operating system has optimization for disk and processor usage.

I would say it is wiser to buy better camera and better capture device plus better encoding software then trying to optimize disk with non server operating system.