I think you can get away with a 9.5lbs 458 Mag quite comfortably. My Mod 70 African originally weighed 8.5lbs and I new that was rather brisk. The load was a 500 grainer at 2130fps. I added a mercury reducer in the butt and some lead in the for end to get the balance back. I initially hated the feel as that lovely handling went away. Having fired the rifle later, I much preferred the new variation. The rifle became lots more controllable and I've got used to the handling since.