> the Mac compatible the card was listed along with Sonnet cards, and was listed as PCI,
> not a proprietary interface. But again, could be wrong.

Wrong for sure. The only Sonnet accelerators for the PCI slot are the Crescendo 7200 cards, which, as said, max out at 500 MHz. There's a Sonnet card series called Crescendo/PCI G4 available at 700, 800 and 1000 MHz, but despite the name, these are not PCI cards. Maybe it was one of these?

> As to the 1.3 GHz cpus I was referring to, that's just the stock of
> processors NXP has left (outside of the 7448). Its surprisingly very few.

This shouldn't be relevant as nobody will seriously want to restart production of any of the compatible cards anyway.

> provide me some info about the PMC cards. [...] references for the PMC cards and the carriers?

See there (info is somewhat cluttered):
http://aminet.net/package/driver/other/SonnetLibrary
https://github.com/Sakura-IT/SonnetAmiga
https://github.com/Sakura-IT/SonnetAmiga/wiki
http://eab.abime.net/showthread.php?t=76633 (start at comment #1447 on page 73)