On a box using 300W at load, the difference between a 65% (460W) PSU and a 85% (353) PSU is 100W. Yeah, PSU efficiency makes a difference.
Are you replying to me? Assuming you are... well, I'm not talking about efficiency. I already stated that it's not silly as long as the PSU is highly efficient. The topic is completely different. The topic is about using over-dimensioned PSUs (say, 350w over 1000w, assuming both are 80%+ efficiency certified).
The question is: if the normal power usage of a certain computer unit is just 200W (actual power usage, not the power draw at the wall, which will be a little higher depending on how inefficient or efficient the PSU is), is there a difference in actual power draw between using an 80% efficient 350W PSU and an 80% efficient 1000W PSU?
My opinion is that it won't matter at all, since both 1000W and 350W PSUs will be drawing ~250W from the wall, since they are both 80% efficient. Voo, however, pointed out that the efficiency of PSU's depend on the load they are in, and added that efficiency is better at 50% or more loading compared to a miniscule 20% load, thereby saying that using an overdimensioned PSU (1000w in this case) will actually be less efficient than the smaller PSU simply because of the lower efficiency in "mini" loads.