Are you sure price per round isn't an issue?
I looked into this also, and the deciding factor was cost of ammo, and availability.
.458SOCOM sells at roughly $3 a round. Too much for my tastes, although I loved the idea of an AR chambered for it. Basically a .45-70 in an AR platform.
.300BLK ammo is much cheaper and very available, and would be a great short/middle distance hunter, as well as a SHTF rifle.
I built my second AR as a .300BLK as a result. For more power at longer range, my next build will be a 6.5Grendel.
