> and unlike Ethernet, all the cards on the ring had to talk at the same speed.

Essentially that was the same for Ethernet too, everything on the same leg needs to talk at the same speed, though IIRC a different speed device wouldn't take down everything, it would just cause a significant excess of collisions due to the out-of-sync cross-talk and not be able to talk to anything itself. It wasn't until switching hubs and full switches were around that you could mix speeds on the same leg (with a switching hub you'd actually have two legs, one at each speed, bridged, with a full switch you have a separate collision domain per port so can mix speeds quite freely).