Seeing as I have just completed a self project of rebarraling a REM 700 338 Win with a new REM sporter 26" 338 RUM barrel I feel ok w/commenting.
The RUM will out do the Win velocity wise by 100+ fps MV with HOT loads in the Win and mild loads in the RUM.
I shoot the 300gr SMK in the RUM @ 2730 MV. With a BC of 0.7+ ~5000 feet elevation and higher it will do in a deer at any distance you can hit it.
With US 869 the 300 SMK is very very accurate and with the muzzle brake
very very pleasant to shoot. 225s and 250s were great in the Win and so so in the RUM. This RUM really shines with the 300SMK.
I am comfortable out to around 800 yds with the rifle but will gain some distance through a little more practice. I'm figuring maybe a 900 yd max due to steadiness of the sporter weight and comfortability with the scope that I have on it.