I've got nothing close to anything as fast as you mentioned, but just
FYI, I did some speed comparisons between the BT-946C and the NCR53C810
on my PCI system.  The NCR was consistently, but insignificantly, faster 
than the BT (about 1%, joy).  Both were about 60%-80% faster than an
AHA-1542CF depending on the type of test.

On another system running BSDI we've used the 946 with Barracuda's (fast, not
wide or diff) and gotten stellar results on DEC PC XL 590s (PCI P90 systems).
Up to almost 5MB p/sec to a filesystem in some cases (large writes to an
existing file).  This is of course with some fs tuning.

-Mark