You are right that the RUM is balistically superior period. But the rum really is at it's best with a longer barrel. I think you will loose a couple hundred fps by lopping off 4 inches. THe WSM or SAUM will loose a lower percentage than the bigger guns. Also, a factory sendero weighs over 8 pounds already, do you want a sporter, or a heavy long range hitter?
You can get a sporter to shoot awsome as long as you limit your shots, don't let the barrel heat.
I used to re-load but now I "hand-load".
-- Well, at least I try