I used U8g2 to see how quickly a Nokia 5110 display could be updated with a 3.3V 8 MHz Arduino Pro Mini. The good news is that it is pretty fast. The bad news is that it's a bit of a memory glutton, consuming 42% of program storage and 24% of dynamic memory. It's probably all the data for the lovely fonts.

Speed will probably roughly double with a 16 MHz board, but there are no 16 MHz 3.3V boards, so that means you'll have to complicate things a bit with level shifters.

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