What's always so amusing to me about these conversations is that nobody ever talks about DISTANCE. I mean, at some point, a 30-30, 303 British, 30-06 and .300 Win Mag are all delivering basically the same bullet with the same energy - only at different distances. For whatever reason, that always seems to be forgotten or ignored.
So yea, if the longest shot one could expect on a moose is 100 yards, then a .303 is more than enough gun. Likewise if the King Ranch is allowing their clients to shoot Nilgai at 400 yards, the I could understand the .300 Win Mag.