I have not shot a bear, or anything else for that matter, with my 45-70 yet, but would not hesitate to do so. I shoot the Marlin cowboy gun and the load is as follows,

1 510 grn paper patched bullet
31.0 grns Reloader 7
OAL 2.560"

VEL @ 15' is 1400fps

I started this process with 33.0 grns of reloader 7, velocity was in the 1600 fps range and recoil was stout to say the least. My personal opinion is that this would do just fine on bear, moose, whales and the like. Accuracy with the 'lite' loads is right at an inch and a quarter using a tang peep and front globe. With the Marlin, full case capacity simply cannot be utilized due to the OAL restriction, if your using a Ruger # 1 though you should be able to genuinely abuse yourself.