I found a couple references in other forums that people were getting 4.4mb/sec (actually kind of surprising its that slow) on a stock A3000 using SCSIbench
A3000 scsi tops out around 5MB/s synchronous so that is pretty close to it.
Its pretty fast for 1988 standards.
scsi on the accelerator such as warp engine etc will yield near 10MB/s
speedgeeks hacks may speed up the a3000 scsi a bit.
You will likely need a faster cpu to get to the magic 5MB/s mark without hacks.