I like double rifles with hammers. They are safer to carry loaded with the hammers un-cocked than a hammerless double loaded with a safety on. Of course some modern doubles have an un-cocking "safety".

I started shooting with a 12 gauge and .410 gauge side by side shotguns with hammers. They are necessarily (edited) NOT slow at all. Assuming the rifle or shotgun can be shot with both hammers cocked. They do take a small amount of time longer to cock and get into action.

Assuming I decide my Westley Richards hammer 10-bore is powerful enough I would use it on elephant and will certainly try it out on buffalo.