I have a little unconventional view on power saving and CPU choice. Recent Intel processors use EIST (Enhanced Intel Speed Step). This drops the CPU multiplier to 6 when the processor is basically idle. Therefore, I prefer a CPU with a slower FSB and higher multiplier because the clock speed is lower when speed step kicks in. Dropping from 8 to 6 is not much of a change. So, from that perspective, I think the E7300, with a 10x multiplier is a good choice. The main drawback is that these processors have small cache memory, so that can definitely affect peak performance.
[Edit] You could also go with an E4600 (2.4G 12x mult FSB-800 2MB cache) if you're not set on a 45nm chip. E2220 is also 2.4G FSB-800, but I think the 1MB cache is a little too thin.