To the O.P
I'd probably go 243 in the Montana given the two choices. More components to be found and more variety of good projectiles. Also reams of good load data. You need to go off the books to get a 257 Bob to be all it can be, if you are new to loading it may put you out of your comfort zone. Having used both I'm pretty sure no game animal can tell the difference.
Sam, are you still shooting 90 grain Scenars in your MT?
