hmmm, i got 18mb/s out of my old quantum atlas2 10k rpm 9Gb drive.
abaout a couple of years ago, i was in a meeting with some raid / drive technicians and they were saying how the firmware for 9Gb drives had pretty much stopped development as hardly anyone was buying them anymore just tweeks to handle 10k 15k rpm spin speeds. if you wanted a drive to deliver a decent data rate, then you had to buy 18Gb or bigger as that was the way the market was going, so then these drives would have updated firmware to properly support the newer scsi interfaces.
so given that the Symbios 770 chip on the cyberstorm was pretty good for the time, to get better rates, get bigger drives. (more cache ram etc.)