> Even if the MorphOS kernel still supports 603/604
> (which it should, but I'm not sure)

As MorphOS 3.18 Beta was shown running on CSPPC, I guess it does.

> PIO0 PATA IDE access

CSPPC has Ultra Wide SCSI controller (40 MB/s with almost no CPU load).

> Cyberstorm being your fastest gfx option...

In case you mean CyberVisionPPC/Permedia2, the show machine was equipped with G-Rex and Voodoo3.