Which CPU's are the most efficient per watt?

Answer 1

Instead of buying an i5-750, you should consider buying a more energy

efficient Xeon X3323:

Much more l2 cache 6 MB vs 1 MB 6x more l2 cache; more data can be stored in the l2 cache for quick access later

Much lower typical power consumption 65W vs 122.45W More than 45% lower typical power consumption

Much more l2 cache per core 1.5 MB/core vs 0.25 MB/core 6x more l2 cache per core

Much lower annual home energy cost 19.27 $/year vs 42.81 $/year 2.2x lower annual home energy cost

Much lower annual commercial energy cost 70.08 $/year vs 122.73 $/year Around 45% lower annual commercial energy cost

Better performance per watt 1.67 pt/W vs 0.89 pt/W More than 85% better performance per watt

Answer 2

The i5-750 and the i7-870 Lynnfield CPUs are incredibly efficient and are probably the best.