ATmega644P vs. ATmega1284P (3 replies)

I bought a used kit that came with a sanguinololu with an ATmega644P. I've seen a lot of discussion about boards with ATmega1284P and I'm assuming it's newer/better/faster. But in a reprap (prusa2) what difference would I really see? Is it worth an upgrade? I assume I could just head to ebay and buy an ATmega1284P and swap it in the socket where the 644p is?

Thanks for the input. -Bret