I own both the 338 & the 300 rum. And the 338 can shoot a 180gr bullet up to 3500 fps and it can shoot the 250gr bullet up to 3000 fps. The 300 can shoot the 180 at 3250 and can shoot the the 220 at 2900 fps.
That would be with a 300 gr SMK or 300 gr ULD RBBT. Basically wind drift and terminal energy for big game is about the only difference between the two. That and the 338 has a significantly longer barrel life if all other things are equal.
Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.
Well....let me give you my view! I've killed whitetails and mulies out to 800 yds. in years past and what I was shooting was just a very good and well built up accurate rifle in 30/06! Nothing fancy...but the rifle was highly accurate and I knew how to hold at that distance. But now...as I'm getting on up there in years..."long in tooth" as they say....and since I've been a "shooter" all my life....I can see the day fast arriving where I may just want to go to the range...sit down with something like a .338 RUM and just "whang" a steel plate from 1500 or so yards! And probably....the .338 RUM would suffice for that instead of something built up on the 416 case! Recoil won't matter with a good brake up front and a heavy rifle so basically it all depends on what one wants to use the rifle/cartridge for! But I can tell you this: "Life's too short just to have a couple of rifles!"