Did you try a .458 300gr bullet in a Harvester Black Crushrib sabot?
That combination is extremely popular in the Savage MLII. Personally i dont care for the faster book powders and a 300gr bullet. SR4759 would be my choice if needed. IMO Reloder7 and N120 are far superior powders when using a 300gr bullet. They yield better max fps and less peak pressure.