
This doesn't sound right to me.  Don't Quadras use the 53C96?  If so, the
Mac has nothing to do with the SCSI timing.  That's all handled by the
chip.  About the only the timing could be wrong is if Apple programs the
clock registers wrong on the 96.  That, however, should only really hurt
synchronous transfer, which is not used by the Mac SCSI Manager.

Furthermore, disabling blind writes should be meaningless on a Quadra.
On Macs that used the 5380, which is a much lower level SCSI chip, the
Mac was responsible for the handshake of each byte transferred.  Blind
mode affected how the Mac handled that handshake.  On the 5396, the
handshake is entirely handled by the chip.