I shoot a Gibbs bolt rifle in .45-70. Those Enfield actions can handle a fairly heavy load. However, I wouldn't go much higher than 54 grains of IMR 3031. I tried 55 grains but the pressure signs were such that I don't think going there would be very wise. But suit yourself. The Ruger is a very strong action and it's quite possible that it can take all that and more. Just be very careful working up loads for it. Remember that a face full of steel from a blow-up isn't very pretty.
BTW. I just put a sportered Remington '03 in to be rebarreled. The chambering is to be .35 Whelen. I think that it's a fine choice for your primary arm. Elmer Keith was right, bigger is better.
Chet
