https://docs.google.com/spreadsheet/ccc?key=0AmSWTZmbKkVhdFFyM3RhUWphY2Nlc3F0dEhtZ3pZR1E#gid=0 I've been benching a lot of PSUs that I have acquired lately (much more than I actually need, lol). I'm about half way through testing them and I thought the results may be interesting to others. No major surprises really, efficiency more or less as expected with older and lower 80+ rated PSUs not performing as well. Also, the 'sweet spot' of the PSU makes a considerable difference to the efficiency so it doesn't make sense to seriously overpower a rig at all. Also shows how much PSU technology has improved throughout the years (or at least maybe the older PSU has degraded). Eg, the very popular 80+ HX-520 which used to cost like $150 is like 6% less efficient at Windows idle load than a modern $80 Antec HCG 520 Bronze.