I have added Atmega1284 to the list of MCUs which can be used in MegaDrum. Atmega1284 allows to save twice as many Cinfigs/Drum Maps in non-volatile memory compared to Atmega644.
Also, with the new USB MIDI firmware and latest MegaDrum firmware it is now possible to switch to higher MIDI speeds which reduces latency by 0.5-1.5ms.
For details see Changes in version 20110424 in Latest MegaDrum firmware version.