B, I've never shot a 300 WSM Montana but have an A7(300 WSM) that weighs about as much as your 8400(just over 7lbs scoped) and it does kick. Not terrible but you do have to 'watch' it every shot.

The 270 84L is about the top of my fun limit, anymore the 300 WSM is a little past fun.


Get the 270!