[paulmd]

aiming for 50-60% capacity during typical operation is the standard recommendation.

Efficiency usually starts tapering off below 50% and below 30% it falls off a cliff - however, that just means instead of an ideal 10W power consumption you're actually pulling 30W or something like that, it is usually not a big deal in absolute terms.

(there are also some exceptions, some of the platium/titanium PSUs actually can hold pretty decent efficiencies right down into the basement.)

750W is a good "standard" recommendation, that's enough for any one GPU on the market.

The rule of thumb is really more to guide people not to buy 1600W or 2000W monster PSUs just because "bigger number is better!".

(Although those giant PSUs do have the advantage that they can often run completely passively under load, they won't kick fans on until 50% or 60% load, which for a 1600W PSU means you can comfortably run a high-end GPU and a high-end CPU completely passively.)