I used an Apollo 1240 @ 40 MHz for a while and I have to say it ran everything perfectly well without any issues. It was also extremely fast compared to my previous card a 68030 at 40Mhz. An 040 blows any 030 clean out of the water.
If 68060's never existed, I'd still be happy with an 040 at 40MHz. But because they do exist I had to get one anyway.
I have to agree with Mechy though.... 060's with naff masks run just as hot as 040's with naff masks (ie fry an egg hot). I have a Blizzard 1260 & Apollo 1260, they could both quite easily fry an egg.