Well, I think I may have this all in better shape. If going off
what my AlphaStation 500 tells me, now that I'm able to read
the NVRAM settings for some isp implementations, DEC has established
non-Ultra settings for some of the internal devices they support.

For example:

isp0 at pci0 dev 9 function 0
Qlogic ISP Driver, NetBSD (pci) Platform Version 0.97 Core Version 1.2
isp0: setting input clock to 60
isp0: Board Revision 1020A, loaded F/W Revision 7.55
isp0: Last F/W revision was 5.1
isp0: interrupting at kn20aa irq 12
scsibus0 at isp0: 16 targets
sd0 at scsibus0 targ 0 lun 0: <DEC, RZ1CB-BS (C) DEC, 0658> SCSI2 0/direct fixed
sd0: 4091MB, 3708 cyl, 20 head, 113 sec, 512 bytes/sect x 8380080 sectors

is what the onboard ISP chip for the AlphaStation 500 reports. A 1020A
is ultra capable, but there were NVRAM settings for some of the targets
set already because rather than setting up for ultra transfers, this
disk was then set to negotiate no faster than Fast/Wide:

isp0: Target 0 Sync Mode at 10MHZ, Wide Bus, Tagged Queueing Enabled

If you still have your Miata, I'd greatly appreciate if you could boot
a NetBSD kernel from me that will see whether I've got things set
correctly at this time.

-matt