Thank you westfw for your reply.
Well, the Arduino Mega (avr1280) also has 128 KB flash, 8 KB SRAM, etc., but as you say is limited to a 16 MHz clock. I suppose that this and the extra timers and UARTs can make a difference.
But the real difference I'd like to see is a port of the Arduino mindset to one of Atmel's 32 bit microcontrollers. This would be a huge increase in processing power when compared to any board in Atmel's 8/16 bit barnyard, and it would open the doors to real time audio and video processing applications.