I was literally reading about about this.
The 80+ rating has to do with the efficiency of your power supply, i've read that some power supplies only get around 50-60% efficiency and lose the rest of the power due to heat. These better power supplies basically are doing less work to get you the power you need, which in turn actually saves you money in the long run. It should be noted that anything passed gold is consider business class equipment and wouldn't serve a normal consumer really any good.
I have a few comments about your file server, i've run a file server for many years. Is this file server personal? Assuming that it is, Why are you buying all this epic hardware to simply share files? You could run a 10 year old computer, and as long as you have 2 gb of ram, with a gb connection, it should run just fine. And to run all this hardware for only 2 TB, it makes no sense to me really, you could put this Hard Drive on your personal computer and simply share it, and as long as your computer is half way decent, you wouldn't see any lag really. Even if they are stream music/movies/docs, whatever.
This power calculator can give you a general idea on how much power you are going to need based on the specs.
Here is my question that i posted yesterday regarding this issue PC power usage related to power supply