If you get one of the latest 68060 it should be clockable up to 100MHz with good cooling (they are only 50MHz parts...). You normally overclock it through the oscillator on the Turbo board - AMIGA turbo boards are not designed for running at such high clock speeds.
I heard that most Apollo Cards are clockable up to 80 MHz, there is someone around here who does 040 to 060 upgrades-he knows better than i.
