>> The same drives that are flaky on my Beige with the Sonnet temp card
>> (and drop back to Ultra/33) run fine - without hiccup - on the G4/AGP
>> on the internal busses.
>
> One thing that occurs to me immediately is:
>
> Do we know what clock speed the PCI bus in this machine is actually running
> at?

That shouldn't matter, but all Macs before the Xserve G4 and PowerMac G5, 
with the exception of the one video PCI slot on B&W G3s and PCI G4s, were 
33 MHz.