Older processors were not necessarily more energy efficient than newer ones. I'm willing to bet you'd get better battery life out of something like a modern ARM

Older processors were not necessarily more energy efficient than newer ones. I'm willing to bet you'd get better battery life out of something like a modern ARM Cortex-A than any 68k, FPGA-implemented or otherwise, and have it be significantly more powerful besides. But IANA processor nerd.