I have been pondering this a bit. It surprises me that the .458 Socom (the slower of the two) is the one that runs rifle bullets. On the other hand, neither are running very fast. I'd like the extra 10% MV/20% KE of the .450 over the .458, but I do appreciate the difference in bullet construction. I'm not really certain that 2100-2200fps is too fast for pistol bullets though? (Thinking back over the last 20yrs pushing 240grn "pistol" bullets out of a Marlin 1894 to 1900-1950fps for deer). Having ran .45-70's for deer, I've seen my share of bullets that were clearly moving too slow to properly expand (rifle bullets).

So the bullet choice IS indeed something that does keep me up at night. Ultimately, I'd like something that would be a modest improvement over a .45-70 for trajectory, plus the semiauto edge. The major advantages being bullet construction in favor of the .458, and velocity/energy in favor of the .450. I haven't made up my mind yet, but I'm leaning towards the .450 because I'm fairly confident in the "pistol bullets" out there, and would prefer the flatter shooting round, but I'd love to hear some first hand exposure for how the .450 is on big game (by Ridge's pics, I'd say the .458 is doing just fine).