if you need performance and money not to much of a concern get a
15k 320 scsi ,also very reliable
seagate website shows a lot of tech info on what to expect from diff types HDD's.fasrter the rpm's faster the seak time
also don't forget buffer size this improves response to.
I see a diff between my older scsi's 80mb/s V my 160 ,320 drives
but I have a seagate iede that rpm's at 7200k and older ibm at 5400 rpm
can't see the diff ,the new serial II's are supposed to be very fast ,your going to pay for those.