have you checked out the vendors - segate, ibm, quantum etc - they usually post their optimistic results.
as a general rule IDE are at about 7200 rpm 8-9 miliseconds seek time, ? bandwith
SCSI are about 10000 rpm and i think up to 6-8 milliseconds seek time, ? bandwith but greater than ide.
SCSI are always the choice when budget allows but ide have been showing great performance for bucks.