George Mallory : biography
Mallory is known to have "swarmed up" a very similar obstacle in alpine conditions on the Nesthorn (3,824 m) in the Swiss Alps, and his companions were under no illusions about either his considerable ability or his visionary, idealistic self-motivation.
As for climbing difficulties, Mallory is known to have climbed comfortably at HVS (Hard Very Severe) standard (YDS ~5.9) in Wales and Cumbria. Many of his early pioneering rock climbs were undertaken on Y Lliwedd, a near-1,000 ft often-loose, usually wet cliff face, which is part of the Snowdon/Yr Wyddfa massif. Those who have climbed on this face in mountaineering boots, perhaps armed with only basic equipment, will understand the genuine difficulty of a climb of HVS standard – and come to truly appreciate Mallory’s boldness and physical ability. But on this, his final climb, he had already taxed himself by a previous aborted ascent, along with the other normal strenuous activities of being on Everest.
There is some evidence available on the rockclimbing ability of Andrew Irvine—but all at sea-level altitudes. In her biography of Irvine (Fearless on Everest) Julie Summers notes that Irvine did climb the Great Gully on Craig yr Ysfa with Odell, a wet, five hour climb of VDiff (~5.4) degree of difficulty. Nevertheless, brief rock climbing episodes in above freezing weather are not like mountain climbing with its sustained, frigid, courage-draining exposures. Given Irvine’s limited climbing experience, it seems unlikely that he would have had the ability to climb the Second Step, and even more unlikely that he could have done so in the rapid manner described by Noel Odell, who witnessed them from a long distance.
The rope-burn evidence on Mallory suggests that the two climbers were roped together when they had their fall at the 1933 ice axe site, making it unlikely that Mallory had made a solo "sprint to the top." This would have involved Irvine waiting at the base of the Second Step for up to ten hours—an impossibility in that weather with their clothing. Mallory could have lost his footing and the rope snap with the tension leaving irvine alone in possible darkness, later possibly giving up and succumbing to the cold. .
Noel Odell believed he had seen Mallory and Irvine ascend the Second Step. The British climbing establishment increasingly questioned this opinion, and Odell eventually changed his story to say it was the First Step. Towards the end of his life, however, he reaffirmed his original view. If his eyewitness report is accurate, the topography he describes appears to fit the Second or even the Third Step on the ridge. Climbers on the 1999 expedition watched Hahn and Anker from Odell’s viewpoint and said that when they climbed the third step it was like watching an "action replay" of Odell’s description of them climbing the second step.
On the other hand, Mallory’s final note describing his assault plan of the mountain had him reaching the Second Step as early as 8 am. Everest historian Tom Holzel suggests that when Odell saw them climbing a Step near 1 pm, he assumed that they were still ascending and therefore must be on the Second Step, as there is no need to climb up the First Step to reach the summit, unless a different route was taken, where you can drop slightly below the 2nd step: climbers typically cross or traverse its base and continue around it. Odell naturally assumed they were still ascending, but woefully late, knowing the difficulties of the oxygen equipment at the time. However, Holzel surmises that they may have already reached the Second Step and turned back, due to its difficulty. By 1 pm they could have been close to estimates of climbing time in their descent from perhaps as high as the base of the Second Step. If they were already on their descent, the unproven oxygen malfunction, and the unlikely late start theories can be discarded. Odell then may have seen them clambering up the First Step as a vantage point from which to view and photograph the complex route to the Second Step before returning to the North Col (which is what the French did in 1981 when they, too, could no longer continue upward).