RE: 270 or 300 WSM
A quick check of the Short Trac models shows the .300 WSM to be the biggest cartridge they offer. Therefore, I'd recommend that one, but I honestly don't think it'll make much, if any, difference in on-game performance under 300 yards. If you really want more oomph, step up to the .338 Win Mag - I think that's offered in the BAR Safari models.
Remember, too, that the 400 yard shots on large game are far more rare than we're led to believe. Consider the terrain where you'll be hunting the elk/moose. I was in Southern BC 2 months ago, & the guide outfitter tells all his clients that they shoot more elk in "self defense" than they do past 300 yards. All told, Isaw 5 bulls within 50 yards.The guidecalled a 5x5 within 5 yards, & I took my 6x5 at 65 yards. That critter didn't laugh at the 165 grain Interbonds from my .30-06.
Just my $.02.
FC