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.
Under Mac OS X 10.3 and 10.4, a volume greater than 2TB will show as a 2TB volume due to a limitation in Apple's ATA layer (just above the driver). Sonnet plans to provide a 10.4 fix in the next driver release. Under Mac OS X 10.5 and 10.6, the full capacity of the RAID volume is available.