Jeffries. There are no reports of him gassing during any physical activity during his athletic prime that I'm aware of. What happened over 49 rounds in Paris in Jeannette-McVey III took place on a cold April evening where both participants were being administered oxygen between rounds. For Jeffries-Sharkey II, a movie light created blast furnace was compounded by Jeff having had his left elbow dislocated by wrestler Ernst Roeber during training in a medicine ball prank gone bad. Deprived of his money arm, Jeff proved he was far more than a hooker by inflicting considerable damage to the left side of Sailor Tom's face and body with his right hand alone. [The severity of the injury to Jeff's left was evidenced by the fact the right side of Sharkey's head and body emerged unscathed from that 25 round war.] Even with all these handicaps, Jeff was coming on at the end, and it was Tom heading for a stoppage fate if that rematch had been to a finish. Give Jeff two good arms and hands, a cool climate, and oxygen [heaven forbid!] in his corner between rounds, and I'd bet my paycheck on him getting the stoppage. Remember, his first knockout of Corbett came courtesy of just one left hook in round 23. Jeff's power would not be diminishing as the match proceeded.
imo, jeffries is the great finish fighter ever among the heavyweights. i think guys like sullivan, johnson, tunney - who had tremendous determination and endurance, marciano, jackson would be great in finish fights. fitz as a middle or lt heavyweight was great at finish fights. i think in jeanettes time, langford and johnson may have won at 20 or to the finish- dont know