You can chase high BC's all you want.. Fact of the matter is that within realistic hunting ranges a critter is gonna be just as dead when shot with either a .40 or .50 BC... Dead is dead...
*WARNING; The post below contains an opinion, read accordingly...*
I couldn't agree more, dead is dead. But just to give you an example of real world numbers with only changing factor being BC.
Using the Barn's 100 grain TSX (.257 cal, BC=.37) at 3000 fps, you end up with 46.67" drop at 500 yards from a 100 yard zero (26" Baro, 60*F). Energy = 862 ft. lbs.
Adjusting that same BC to a .6 results in a drop of 39.82" with those same conditions. Energy is right at 1211 ft. lbs
Stretch that distance out to 700 yards and you end up with numbers like this:
BC= .37 Drop is 119" and 591 ft. lbs energy
BC= .6 Drop is 95.7" and 977 ft. lbs energy
Obviously anything under that normal 400-500 yard range is going to be a moot difference. Stretch it out there a little bit and you're setting yourself up at a disadvantage imho.
That's just to give you an example of what a higher BC will do for you in energy retention and velocity. Like you said, dead is dead and most guys won't ever shoot anything over 400 yards. However if down the road someone wanted to stretch their range out there with practice and possibly hunting situations, you would be limiting yourself by starting out with that .257 caliber. Same reason why you hardly see any guys shooting the .270 calibers at distance. Relatively poor bullet selection. There are a few .270 bullets out there with high BC's, but they are expensive and not available everywhere.
168 Bergers, 180 Bergers, 162 Amax all have G1 BC's over .6, if starting from scratch and hunting big game is the goal, why would you limit yourself starting out with a limited caliber? Will it kill game at distance? Sure it will. Is it the best choice? Probably not. In the field long range is all about reducing the margin of error. Between environmental conditions, shooting angles, thermals and winds there are many things that can affect that error margin. Having a high BC bullet will not replace knowledge and practice, but will allow you more wiggle room for sure.
This is only my opinion, and please understand that my opinion reflects my passion for long range shooting and is therefore bias. People can throw numbers out there all day long, but if you can't shoot the gun then it don't mean anything.
If just starting out searching for a good factory caliber that isn't going to break the bank shooting, I would look at a .243, 7mm Rem mag, 7 WSM. Easy to find factory ammo, and great velocity and high BC bullets.
Mike