I use a .300 win mag, and so did most of the guides in the elk camp. The other guides all used 7mm mag (except 1 who used a 280 rem with 140 grain corelokt).
I don't know how your finances are but weatherby calibers seem to be twice as much or more than standard calibers. Not a prob if you reload, but I think a box of factory 340 W-Mag would be 60-80 bucks. I think the rem ultra short mags are pretty pricey too. The old standby 338 win is reasonable and effective, and I hate shooting it. I have arthritis in my shoulders and I am only 43!!! Actually if I were firing at game, I wouldn't notice but there is the bi yearly sight in and practice.
I just fail to see how a .300 win mag with 180 grain nosler portitions can be beat. I have a friend who swears by the new 325 wsn.