Impossible to say with any certainty since we do not have clear film of Jeffries. Certainly what we do have looked at critically he looks very good. We do know Jeff was considered an ATG for many decades. If I had to pick a winner I would go with Jeffries as a prime extremely conditioned two handed puncher. I would think Jeffries could keep Joe at bey with his great strength.
Stories of Jeffries athletic feats do get embellished somewhat, but even if we just go with what was witnessed by reporters, we are obviously looking at an exceptionally strong heavyweight. For example one part of his training camp, was that he used to lift and moved around a 300lb bag of sand. He was clearly more George Foreman than Joe Frazier in terms of physical strength.
That's the problem when they about talk about his great strength.How effectively was it applied?We know he laid on Corbett and Fitzsimmons in the clinches using his extra weight to tire them, but we have no recorded instances of him manhandling them.