Orville, the 243 might be a better option for the Kimber 84M action.
I have both and haven't run into any problems loading for either but the 243 will give you more room to work with.
And unless you plan on shooting a lot I don't see barrel life being an issue. And of course if you do get wild and burn it out it could always be re-barreled.
As far as game goes I think you'd have to step up to say a 270 in order to see much difference.
