There were cards that had a pot on the back. You could just dial up more speed, until your machine ran poorly, then back off just a little. Kind of crazy to think about!
The speed on my Apple FastChip is adjustable in real time too. It's neat to just dial a speed appropriate for the application at hand.
If you are interested in programming your Apple in assembly, you can ask nicely for your FastChip to include a 65816 processor. It's going to act like a 65802, due to hardware limitations, but otherwise yeah. You get the 16 bit instructions to use.
I've not had any compatibility trouble with mine, which is a 65816.
The speed on my Apple FastChip is adjustable in real time too. It's neat to just dial a speed appropriate for the application at hand.