i dont think the psu really matters honestly. dont waste money on anything crazy. just get a decent well priced unit and you will be fine, just wait for KNC to tell us the specs first.
A more efficient PSU should give you a longer tail--but that's also when you're earning the least, so perhaps it won't matter quite as much, much as you suggest here.
These are the best power supplies you can buy, I think. I have them running in multiple computers and they run so efficient the fan barely ever comes on to cool it. Never really maxes out and they aren't over powered for the system at all. Trust me, these are high quality power supplies.
http://www.seasonicusa.com/