I spent about 3 months trying to decide on the rifle to buy that would work for primarily deer, and the occasional elk and occasional pronghorn. I ended up deciding on my Browning A-Bolt Stainless Stalker in 7mm Rem Mag as my one all around rifle. So far after taking 2 deer, a pronghorn and an elk I have been very happy with it's performance. I think that by sticking with one gun I will be more comfortable and accurate with it. If I had an elk rifle I would probably go with a .300 Win Mag or maybe give in to peer pressure and buy a .300 WSM but for now I think my 7mm Rem Mag will continue to serve as my all around gun. Sure it is a little overkill on whitetail deer and antelope, but I can live with that. I think with the right bullet choice it is perfectly fine for elk and the elk that I shot this year agreed.
My friends son has a .338 magnum that he uses for elk hunting and he shot 5 times at an elk with it and hit it once in the guts and knocked off one side of his antler and missed the other 3 times at 150 yards. Of course I think that is more from him getting exciting than the caliber of the gun he was shooting!
I think there are folks on both sides of this arguement that like to stroke their own egos. Folks who like to brag about the "hammers" they are using, and folks that like to brag that they shoot so well that a .270 is all they will ever need to kill an elk. I think the majority of folks are somewhere in the middle.