68060 vs 68040

[Karlos]

Performance wise, there is no contest. The 060 is significantly faster per MHz and the slowest one available already starts at 20% higher clockspeed than the fastest non-overlooked 040.
That said, I find my humble 25MHz 040 adequately fast for my 68K needs. It's a lot faster than the stock 020 my machine shipped with.

[Karlos]

I 100% agree with that.

Even at full CPU use, my 25MHz 040 on the BlizzardPPC is comfortably warm to the touch. My slightly OC 28MHz Apollo 040 is no warmer.

040 boards have a bad reputation, but as has been said, if you have an ample power supply they tend to work fine.

My oldest 040 board is a bit wrecked but that was mechanical rather than thermal

[Karlos]

Well, an 060 will certainly give you the best performance, but expect to pay handsomely for it