There's a few "thumper" round (.458 SOCOM, .450 Bushmaster, .50 Beowulf) threads in the rifles forum, but generally that isn't the forte of TFL. AR15.com has an entire subforum dedicated to AR variants, and that has a wealth of info on the various choices.
The ballistics of the three thumpers are not that terribly different; .458 has the most to offer a reloader at the cost of factory support, .450 has more available factory ammo but not too many variations in bullet weight available, and the .50 just seems to me to have the drawbacks of both (not much factory ammo out there, not reloaded all that economically). Still, any of the three will be very effective at under 200 yards on most any game you're likely to find in North America. If you want longer range, you're going to need to look elsewhere; the design of these rounds (large diameter bullet + need to fit through a magwell sized for the 5.56x45mm) pretty much means the aerodynamics of the bullets aren't too hot. It doesn't take too far for them to start dropping speed and falling back to earth rather rapidly.