RE: Which Gun to drop them down??
I don't know why this keeps coming up either. Bullet/caliber selection is important but it has more to do with shooting skills! I have had only one time where the cartridges I was using was not worth a dime and that was way back in the seventies.
As far as long distance shots, certainly feasible and have been done quite a bit. I shot a antelope out to 437 yards in Montana with a .243 so it is possible. Did the animal drop in it's tracks, nope, but it only ran about 50 yards, stopped and then slowly collapsed.
Shot placement
Shot placement
Shot placement