In a GVP impact series II, if you get 3000KB/s you are very lucky.
On my amiga 500 with GVP Impact Series II Card (A500 HD8+), 9MB of Ram and 68010 I get around 1999KB/s (acording to sysinfo benchmark) with IBM DCAS-32160 SCSI2 HDDs of 2GB.
I have guru rom (omniscsi.device is faster and supports bigger drives) instead of gvp rom (gvpsci.device)
Why don't you visit Ralph Babel page?
======http://babel.de/amiga.html
Regards