Dont forget that the base and rings you use will insure that your scope stays put and true. I would recommend any good one peice base (1913 picatinny) to fit your action and a good set of rings. If you spend good money on a tactical scope, I recommend LaRue or Badger they are the foundation and interface and they matter!
Also, if you pick a Nightforce I would recommend a 50mm the 56mm is too big for tactical / feild use. Larue has a nice combo with a zero stop (second link below), also necessary for quick range adjustment. Note, a S&B requires 34mm rings, not standard 30mm. Hope the links below help.
Larue links
http://stores.homestead.com/Laruetac...tail.bok?no=35
http://stores.homestead.com/Laruetac...ail.bok?no=216
Badger links
http://www.badgerordnance.com/productgroup.php?id=rails
http://www.badgerordnance.com/productgroup.php?id=rings