I wouldn't say Quake was 060 only. I play it on an 040/25 and it runs ok... Well, it's playable. And I also played AB3dII on the same set-up.
Feasibly, unless a game is compiled to run specifically on 060, then it's not 060-only.
However, I agree that you have to take playability into account, and stuffing Quake through anything less than 060 may not necessarily give you much of a 'game'.
So are we looking at FPS, texture-mapped games only? I can't think of any other genre that requires the 060 specifically. Happy to be told otherwise, though
I enjoyed Genetic Species