I feel that distance is actually relevent.
How many of you guys are confident of hitting the brain of a charging buff at 40 yards, especially if he is coming at you through scrub and not open ground.
I mean we're talking about offhand shooting under duress a moving target area not much bigger than the butt of a baked beans can!
It's a lot easier to hit at 15 yards than at twice that distance!
Also much would depend on if you are the only shooter or if you are being backed up by a pro.
IMO trying to work a bolt as fast as you can in order to fire the maximum number of shots during a charge is a good way to get into deep trouble. (if you are not being backed up by a competent PH.)
One shot placed as best you can, and another instantly ready in case you need it, is my choice.

The double rifle is made for this type of work and is far more suitable than a bolt gun.
But, the double must fit you perfectly and you must know how to use it properly and also know where it shoots at 10 yards!
Most owners seem to be posessed with getting tiny groups at 50 and 100 yards with their big doubles and would not have the faintest idea where their guns shoot at 10 yards or less!

So even though I love the 458 and have used one quite a bit, my choice would always be the double even if it was only a 9.3 so long as the gun fitted me perfectly and was 100% reliable.