Powder, Brass life and magnum match prmers and not to mention barrel life are going to cost you more in the long run to basicly shoot the same yardage at 100-1000 yards with a 308
I have got as much as 6 loads and as little as 3 from magnum belted brass.
I have got as much as 20 neck sized loads from lapua 308 brass.
43-45 gr vs. 70-75 gr of powder at 7000g per Lb almost doubles your powder consumption.
a 338 is in a different world, bullets, brass, powder....close to $3 buck a pop if reloading with match bullets, and will be well over $100.00 if you buy them for 20.
But a 338 is for beyond 1000 to a mile 1760 and than add some, when the 308s run out of poop! ( I shoud not say that its not quite true, some 338 bullets have good BC and buck the wind well and make a good mid range hunting rig with lots of energy) But other than that $
I know some guys that shoot 1000y and most shoot 6 brs 6.5s or 308s
Ballistics wise you can push a bullet farther with the extra velocity of the 300 wm, but I am not sure how accurate it will remain past the 308.