Some people have overclocked the 060 to 80MHz and one got to 100MHz with the FPU not working. That makes a very fast old Amiga.
A real rev6 68060 will do 90-105MHz with FPU. Few 68060 accelerators can get the maximum CPU clock speed and maximum memory clock speed out of them though. I have a CSMKIII with rev6 68060@75MHz and 50ns SIMMs that gets the full memory potential but leaves 25MHz on the table. The Apollo accelerators get full CPU speed but the memory speed is not as good as my CSMK3. The fpgaArcade and Natami 060 cards should get the full potential and be quite fast. I expect the computing power to be competitive with most Amiga classic PowerPC accelerators despite theoretical numbers where RISC looks good. The 68060 is very fast in real world code and is much easier to program.
There is still talk of making an FPGA accelerator card which would give you an 060 @ 200 or 300Mhz.
Most reasonably priced fpga processors could achieve about 68060@100MHz speed. It's possible to do a faster cut down 68k processor but the most powerful 68k will be clocked lower and do more in parallel. An fpga processor could be enhanced with new instructions and addressing modes, code combining/fusion, bigger caches, a link stack, etc. that the 68060 does not have but most existing fpga processors aren't superscaler, don't have an MMU or FPU (but 1 is planned) and is not as fast at multiplication, shifting and muxes as the real 68060.
I remember years ago there was talk of using the Freescale Coldfire chips.
The early ColdFire processors were not very fast or compatible to the 68k. The later are faster but still not very compatible. The CF line doesn't seem to be going anywhere from here so looks like as much of a dead end as the PowerPC. The fpga processors could surpass the CF in performance in a few more years.
