Since I started a lot of this, let me say my couple of cents worth......
;-)

- My reading of the specs says that an early 90's ATA-2 drive can easily
saturate the qbus in raw transfer rate.

- If we were worried about performance we would not be messing with
VAXen and PDP-11's. ;-)

- MSCP is cool!

- MSCP is too complex for a few hobbyists to do in a reasonable amount
of time.

- Writing an EIDE driver for the various VAX and PDP-11 OS's still in
vogue, is less effort than writing a faithful MSCP server. Especially
since a true specification of MSCP is unavailable.

- If you are looking for a replacement RD54 for your RQDX3 you will not
complain about performance.

- I am probably wrong.

-chuck