Yup.I think HAMMY said 10mhz was the sweet spot. I know you need the clock but do you also need to replace a 6800? I might have some 10mhz 6800.
Correct, try your original CPU at the higher speed - there maybe no reason to change it.EDIT: Misread what you said. From what I can tell you don't need to replace the CPU if you have a slower one, only a clock and some extra jumpers or logic.