let's sum this discussion up.
1) 450 marlin -- good round or not?
-----yes-------
2) 458 wm -- more powerful?
----yes, fpe wise----
3) 450 marlin -- powerful enough to kill anything that walks?
----yes and proven beyond a shadow of a doubt. nothing left to discuss here.-----
4) 416 more powerful than a 450 marlin or 45/70?
----sure, fpe wise, more effective on a cape buff at 100 yards, debateable.
5) a marlin guide gun more packable and quick than any bolt action the above rounds are available in.
----yes, pretty much not in doubt either.
6) are there advantages to both sides?
-----yes, and which appeals to you is up to you and doesn't make you an idiot if you pick on the side of the levergun and doesn't make you unknowledgeable even if gemsbuck says so.
7) are the regs on dangerous game with fpe limits in some countries pretty much stupid.
-----yes

which calibers would i want in a charge?
----ANY I COULD RELIABLY PUT IN THE CNS, if not then you're in a bad place, just watch mark sullivan hit a cape buff in the chest with 2 600 nitro shells and it doesn't miss a beat!!!!!!!!! so you would i trust a levergun with a 450 marlin hardcast as a stopper, you bet, as long as i was quick and accurate with it and could hit the brain.