The downside to round ball is that they shed velocity/energy quickly. The ballistics tables tell me that a 54 maxi ball driven with a stiff powder charge from my short rifle still has over 1000 ft lb at 100 yards. A ball with the same charge is more like 600 ft lb. Granted, the energy numbers don't tell the whole story, but they are indicative. I would take a 100 yard shot at a deer with a round ball. For something bigger (bear/elk) I think a conical makes more sense.
The doe I busted in the river was 115 yards away according to the rangefinder. Along with all the other stuff that I did not like about taking that shot, that was just far enough away that I probably would have passed on the shot even on dry land.