Although I don't have a .45-70 barrel for my Contender carbine, I'm loading Hornady 300 gr. bullets at an estimated 1500 fps in an older Handi rifle without a recoil pad and they are not too bad to shoot. I have shot 405 grain cast bullets at lower velocities without problems also. I would expect that the Contender would work just fine with the lower velocity loads that you want, and it would not be worth getting an Encore just for this purpose.
I am kind of on the same path as you are and am looking for a .30-30 barrel for my Contender carbine so I can play around with low to medium velocity cast bullet loads for much of my shooting. Who needs a .375 whiz-bang super magnum? I intend to set the scope base forward with a pistol scope in a "scout" configuration like I have done with my .45-70 Handi. It works really well and you never have to worry about getting whacked in the head with the scope.