Being a CO guy, I have some sense of western hunting. My two medium to large game rifles are a .308 Win R700 and a .30-06 Spfd Savage 116, each equipped with Zeiss Conquest 3-9x40mm scopes with Rapid Z600 reticles. I've sighted in each for a 200 yd zero and practiced with each out to 600 yds so I know relevant sighting adjustments for long shots. Both of my rifles shoot to less than 1MOA with 168 gr match ammo (from a Caldwell LeadSled), and a bit more with hunting bullets. Now, since the vitals of a decent-sized deer is a 6-9" area and I don't like lugging my LeadSled on my back in the field, I'd feel less than comfortable with a shot longer than 400yd. I'll leave the really long shots to others. Out to 400 yds, .308s and .30-06s in the 165 to 180gr range still have killing power, and don't beat me up when I practice, which I try to do at least monthly. I've shot .300 WMs and, while there are some advantages for really long range shooting, I find the recoil unpleasant and would not practice with that cal as much.
All IMHO and YMMV.
FH