But it is not like the ATmega1280 at all - they have the same flash memory, that is all the 128 in front tells you. The 1280 is part of the Mega0 line, which has buttloads of ports and innumerable peripheral features not found on any DIP ATmega. The 1284 is part of the Mega4 line, which is just a better version of the Mega16 and Mega32. But yes, it is the most powerful DIP ATmega out there, so it would indeed be the closest choice - just not a cousin.