Some of my most accurate barrels have been the original octagon, including .22lr. I think the potential accuracy of the pistol is same regardless of bull or octagon. Some barrels are more accurate than others, but I think it has more to do with chamber/throat/bore alignment, chamber size, throat conditions, crown, etc., etc, more than the actual profile of the barrel. Now....all that said, I, the 'ol nut behind the butt, can shoot the heavier bull barrel better than I can the octagon barrel in most instances simply because I can hold it steadier, not because that particular barrel is more accurate.
Walt