Ya know they make 80Mhz 060's, right?
Well, there are no "factory" 80mhz chips, but
certain mask revisions are capable of handling
the speed at the cost of longevity.
The later "G65V" mask (MC68060RC50 "A" chips)
are the best canidates for 80mhz, as it seems
the FPU has been slightly modified to reduce
potential errors (as well as MOS11 fab).
Unfortunately, all of the factory 60mhz chips I have
seen (including those with '2002' stamped on them)
are still manufactured with the previous F43G mask
process, and usually crap out at anything above
70mhz.
Motorola makes:
-50 and 60mhz chips with "full" FPU/MMU
-for "embedded" applications, "cut down" 50, 66
and 75mhz chips which lack either FPU, or both
FPU and MMU.