I bought a 700 LSS in 300 RUM about 6 years ago and burned the barrel out in 2 years of shooting. I shot mainly 200g AB"s at 3200 and 210g VLD's at 3000. It was a very very accurate rifle for a factory sporter and would consistently hit my 15" plate at 1K. I killed a few elk with it, furthest was 525 yards, and those 200g AB's were hammers.
However, when the barrel went south, it was time to rebarrel to the EDGE.
The 300g SMK just cant be matched by any 30 cal bullet for retained energy or wind drift. This is what you want in a LR rifle. Who cares how flat they shoot...
If it was me, I'd go the 338 RUM and stick a 225g AB in it and be completely happy out to 1K.
However, as someone stated earlier, run the numbers with the 300 RUM/200g AB and 338 RUM/225g AB and there aint a bit of difference between the 2 really out to 1K. The real difference is when your able to stick a 300g SMK in the 338, then you can start to see why they shine at 1K due to the .770 BC. In all actuality, the 30 cal bullets usually have higher BC's then 338's, except for the 300g SMK, and can be driven faster which results in flatter shooting is all.
I've shot 2 elk in the last 2 years with my 338 EDGE and the 300g SMK at 2850fps. First was a spike at 915 yards, misjudged the wind a bit and hit him a bit forward then I would have liked, base of the neck/shoulder but it dropped him on the spot, and exited leaving about a 1" hole. My 6x6 was shot this past season at 498 yards and hit him right behind the shoulder, and exited the offside shoulder leaving about a 1.5" hole. He ran about 20 yards and was toast.