Here's how I suggest a guy should find the longest range he is competent to kill a big game animal.
Go to the range and pick a target for your cold bore shot as far out as you wish. Do everything as well as you can to make a first round hit; range is known, read the wind like you would in the field, shoot with your dick in the dirt.
Fire the shot and look at results.
If you make a hit, move out the next day or pick a day with tougher wind conditions and repeat. You'll soon find your realistic range limit on game.
Shoot a lot of long range practical rifle matches and precision rifle matches. They will make you a better hunter
Great post and I'd like to add that you should do more at the range than just fire from bipod or off of your pack, as that may not be possible due to terrain masking. You should KNOW what size groups you are capable off from:
1) Bipod
2) Prone slung and un-slung
3) Pack-prone
4) Pack sitting
5) Sitting
6) Kneeling
The latter positions will open up your group. You should already have a ballpark number in your head for each position that you've practiced from. When a yardage appears in your rangefinder, you should know what positions are feasible for YOU to make the shot.
The Army's doctrine with the M24 SWS in 308 was, head shot capable to 300yd, torso to 600yd. Anything further was considered "harrassing fire" and a low percentage shot. That was in pre-laser days and really top shelf shooters could push out another 100yd past those minimums. That was with an MOA rifle/ammo system each shooter had spent 6 fifty hour weeks and launched 2K rounds through.
Everyone in this thread would be a better rifle shooter if they'd spend a week at Gunsite's 270 or attend one of Randy Cain's Practical Rifle classes. How many here know what groups they are capable of from the Hawkins position?
