Ream it out to 445 Supermagnum and leave the barrel full length. That will maximize the velocity attainable from the 445 Super Magnum and you can load it hotter than it is in a factory revolver. The softness of the brass case will be your limit and any other pressure signs. Keep a sharp look-out as you work-up your handloads.
And the 44 magnum can be shot in the 445 Supermagnum chamber so you lose nothing and gain more.