From 0-800 a .308 will do well. A 300WM some would consider overkill, but that isn't necessarily a bad thing. However you are going to go through the barrel faster and recoil is going to be much heavier than that of a .308. I have recently made the transition back to .308 from 300WSM because of expense of shooting and a desire to shoot more comfortably for longer periods of time. Not to sound like a sissy, but the WSM would get a little much after awhile. Not to mention the barrel heats up quicker and brass life isn't up to par with where I would like it to be.
The .308 will serve you well to 500yrd and further if you choose to do so. It is a great trainer for long range shooting. It is cheaper to shoot and the barrel will last much longer than any 30 caliber magnum. If you want a nice comfortable gun that is going to last through thousands of rounds the .308 will get the job done. If you plan on shooting to 1000yrds for varmint and target the .308 will fill the bill. The 7mm-08 can be added to the list I am giving at the moment. If you plan to regularly try and shoot 700+ yards on game (which you will get there eventually, 500 is merely a taste) then the 300WM would be the better option for hunting large game. I hunt with a buddy that has a Lapua, so we plan to use that for the really far shots, and I plan to use my 08 for 800 or less.
Tank