If you want a long range Elk rifle under 9 lbs to reach out to 800, I am sure that any of these will do the job with proper loads. However, IMHO the 300 wm has an advantage in using 200 and 220 grain bullets for the long range hunts. if you can build a rifle light enough for your taste and if you can put up with the additional recoil, I think there will be a small advantage to going this route.
As for the Belted part, couldn't say since I've never loaded a belted mag and only loaded the 300WSM out of the three you selected.
I will admit that I don't have extensive experience, but this is my opinion from a balistics point of view.
BTW, if you are spending lots of $$$, there are many many more cartidges that will have other advantages or disadvantages. how long do you need the barrel to last? try the RUM or the AM's. If you don't mind the recoil, a 338 may be what you are looking for.
I used to re-load but now I "hand-load".
-- Well, at least I try
Last edited by britz; 10-14-2007 at 12:10 AM.