just an idea, but check you have 80-pin cables, and not 40-pin on the hard drives. Not sure if this puts a limitation on how the drive params work?
There is also some other tweaks you can do from disk i/o. (the brackets are my comments)
hdparm /dev/hda (read current settings)
hdparm -c3 (32 bit transfer) -d1 (dma) -X69 (udma5) -m16 (transfer 16 sector not 8) -u1 (mask interrupt) -a16 (largefileoptimised) -W1 (write caching) -K1 (retain this setting if software resert or error)
I would test each element individually though [AND BENCHMARK]. We found that a combination gave up to a 40 percent in increase in performance. But DANGER overdoing it can damage the drive I think. (The one time things went fine UNTIL the acpi tried to spin down the drive, and then it all went crazy starting and stopping and clucking and clicking and it hanged up, that drive is still going, but very flaky -)