Ballistically, they'll be close enough. You're choosing a 7mm magnum, as good as it gets. So since you're not really concerned with ammo, what I would do is choose based on balance and handling. The WSM will be shorter and lighter, the 7RM longer and heavier, obviously. I would get your hands on both and decide which one will suit your hunting style better. I shoot a 7RM, but would love to have a 7WSM too.