The standard 1-10 twist will easily stabilize any 300 gr lead core/cup jacketed bullet on the market. Especially using a 338 RUM or larger chambering. I would recommend going with a 1-10 twist. It never fails that you may get an itch to try the big 300 gr bullets and you would need the 1-10. THe 1-11 would be just fine for the 250 gr if that was the only bullet you would ever use but why limit yourself that way.
A 1-10 twist will also shoot the 250 gr pills extremely well. Groove design is more a personal preference more then actually seeing one design as better then the other. IF the barrel is made properly from a good barrel maker, it will shoot if installed properly, no matter what groove and land design is in the barrel.
If you want to be able to say you have a 5R barrel, go for it but I have never been able to prove to myself that they are any more accurate then a conventional 6 groove barrel of top quality.