Two extra screws is a good idea. For scope bases/rings, I'd recommend SSK Industries' T'SOB base/rings with 4 rings.
As for aluminum not shearing off screws, etc., that's a bunch of baloney. Neither aluminum nor steel rings will shear off the screws. A fair number of types of aluminum bases won't hold up to 460 S&W Magnum recoil. Also, be sure to use low or medium strength Lock Tite when you attach the base; you don't need to use it on the rings.