If so, I am wondering if it became unstable after doing it. I am considering a hack where I can switch between 5V and 3.3V operation since it is a PITA to have to keep adding CD4050s to my breadboard to talk to 3.3v stuff. It seems like everything I am working with lately is 3.3v. But I would like to retain the 5V function just in case (since using a 5V device on a 3.3V arduino would likely damage the Arduino.)Anyway, just curious if anyone has tried this. Obviously the "recommended" voltage for 16MHz operation is 5V, so that is my biggest concern.
I haven't done it with a Mega2560 chip, but for the past year, I've been running the 328chip at 16Mhz and 3.3V, and the past month been doing same with the 1284P chip. And no problems, although against all warnings - of course. If you interpolate the operation curves, they actually show 13.3 Mhz at 3.3V, so you're only overclocking by 20%.Also, for hacking, the 40-pin DIP 1284P chip is a nice choice inbetween the 328 and 2560,and lots easier than tiny smt pins. You get 32 I/O pins.