Our testing has shown that a four-drive array will sustain maximum reads and writes of about 200 MB/second in a 64bit, 33MHz PCI slot. An eight-drive array will not provide any additional performance beyond that of a four-drive array in that slot. To get significantly more performance, you need to use a machine with a PCI-X slot.
Another manufacturer's previously-installed SATA driver may be accessing a Sonnet SATA card in error causing a drive access slowdown. For example, we have seen Fusion D400QR5 performance drop from 200MB/s to under 50MB/s in such circumstances. The solution is to remove the other manufacturer's SATA driver.
