I bought a Weatherby Mark V in 1970 in .30-'06. I got the option with the #2 profile, 26" barrel. My handloads seemingly ran a couple of hundred feet per second faster than most published numbers, due to the longer barrel. While I have never shot beyond 500 yards, I've been able to shoot sub-MOA groups.
Aside from my own deer killing, on loan to a friend it accounted for an elk.
Bunches of hunters kill elk with .308s. Quite a few people compete successfully with the .308 in 1,000-yard competition.
Yeah, the .300 Win Mag will do a tad better, but it's much less pleasant to shoot from the bench or from prone position. Not nearly as much fun, and not that much higher a percentage in actual performance.
I go along with jmr40's comment about buying a good rifle which fits--adding that a long barrel is desirable--and a decent scope. Yeah, you can always upgrade the optics.
After all, it takes a good bit of learning to be skilled at shots of 400 yards and more...
I know from experience on my range that 10X is plenty good for 500 yards.