I know that the xmega is 3V, but all of the logic on the RAMPS can be made to run at 3V with no problem (simple re-design). Makes supporting an SD card easier in fact since no level converter is needed. And you CAN drive most 5V lcd's with 3V logic since they are write only. The step sticks are all 3-5 volt logic compatible. I wasn't thinking of using an existing RAMPS, but rather designing a new board like RUMBA with everything on one board.
The ATxmega128A3U has 8K of sram, the same as the atmega2560 so it will work fine, just can't implement large caches. The built in USB is no slower than the Tensy2.0+++ used on the current makerbot boards, and I'm not talking about LUFA, but Atmel's own USB library (which is also open source BTW,but NOT GPL. It's still free for Atmel chip users.)
The 64 pin chip still has more available I/O than the atmega1284, though not as much as the Arduino Mega (though the Mega board leaves out about 14 I/O pins from the cpu that go nowhere to available connectors).
The ATxmega128A3U has 8K of sram, the same as the atmega2560 so it will work fine, just can't implement large caches. The built in USB is no slower than the Tensy2.0+++ used on the current makerbot boards, and I'm not talking about LUFA, but Atmel's own USB library (which is also open source BTW,but NOT GPL. It's still free for Atmel chip users.)
The 64 pin chip still has more available I/O than the atmega1284, though not as much as the Arduino Mega (though the Mega board leaves out about 14 I/O pins from the cpu that go nowhere to available connectors).