lets see, I have one of the bugged P66's.. and 2 of the AMD 486's that ran past 100Mhz... I'm not sure of their exact speeds though.
The 60, 90, 120, and 180(Pentium pro) all ran on the 60Mhz bus.
The diff between 20 and 33mHz bus was really moot... if you wanted, run the FSB at 75 and get a...