Since the ballistics are so close together, and the game unlikely to tell the difference with most bullet weights used, the big + sign goes to the old standard chambering. Being able to easily procure brass or good, accurate factory ammo in a pinch, outweighs any paper advantage of the slightly, larger capacity round, a handloading proposition from the get-go, just to obtain similar performance.
: With today's range of powders, there isn't very much difference in velocities with standard weight bullets. At the capacity/performance level of the H&H round, it takes a LOT more capacity to gain a worthwile increase in velocity. The Improved .375 case is too small to do this. I am referring to a useable increase, not the mere 100 to 150fps it does give.