>> Sonnet PCI cards (i.e. Crescendo 7200) max out at 500 MHz.
>> Faster cards supported by SonnetLibrary are not Sonnet cards
>> but various PMC cards to be installed on a PCI carrier board.

> The card I was offered via eBay was listed as a Sonnet card pulled from a Mac clone.

Only PCI cards (or non-PCI cards on a PCI carrier) are of use in a PCI-enabled classic Amiga. Faster than 500 MHz Sonnet cards are not PCI but for proprietary Apple connectors.

> If the listing was incorrect, at least it made me aware of the availability of 800 MHz card.

If the listing claimed it was a PCI card, then it definitely was incorrect. Overall, non-PCI Sonnet cards go up to 1.8 GHz.

> I you now state that there were 1 GHz cards.

As I wrote, these are not Sonnet PCI cards but various (non-Sonnet) PMC cards to be installed on a PCI carrier board. The support library is called SonnetLibrary simply because it all started with Sonnet PCI cards. Most cards currently supported by SonnetLibrary are non-Sonnet cards, though.

> the few G4 level cpus still available range around 1.3 GHz (unless you include the 7448).

None of these Sonnet cards are PCI so irrelevant for PCI-enabled classic Amiga.