From the 68K series datasheets:
68060 4.9 Watts @ 66 MHz
68040 6.2 Watts @ 40 Mhz (worst case)
68040V 2.0 Watts @ 33 Mhz (3.3V part)
68030 1.9 Watts @ 50 MHz
68020 1.4 Watts @ 33 MHz
68000 1.2 Watts @ 20 MHz
Coldfire
MCF5407 0.5 Watts @ 54 Mhz external, 162 MHz internal
The 68040 wins!
