mcnobby:
... reduced some of the specs on devices from 20MHz down to 16MHz..
Which ones specifically? I checked the 328P and my favorite 1284P. Both are 20MHz and additional about 40 mega and tiny MCUs.
Which mega with 32MHz did you use? Try to check the ADC. I doubt it will work reliably - sample rate and the highest resolution. I tested 1284P. It seems to work reliably just up to 25MHz.