There you have it!
Drew, thanks for the calculator.
I do suffer from a touch of magnumitis from time to time but I had mostly come to the same conclusion.
I will settle with a 1 oz. load of 6.5 nickel plate shot at 1250 fps and save my 114 year old gun a 53% increase in free recoil.
Really not worth beating up the old girl for one or two decimal places of energy downrange.
In answer to my own question, the increase in velocity is significant!