I agree almost entirely with Richie. The part that seems somewhat questionable is the speed of the steam drill.
Claims and reports on that vary a great deal.
However, several sources that ought to have been well informed put the practical rate in the hardest rock at about 1 in/min.
Also in the hardest rock, good steel drivers on double-jack teams could do about 0.5 in/min.
If John Henry were an exceptional steel driver, which is what is said in ballad, legend, and testimony, perhaps he could have approached 1 in/min.
We don't know exactly how long the contest was, but it seems (from testimony and ballad) that it was an "all-day" contest under the usual working conditions. That immediately distinguishes it from the very popular Western rock-drilling competitions, in which each double-jack team drilled for a specified time, usually fifteen minutes and rarely, if ever, longer. In the Western contests, both members of a team were expert drivers and shakers, and they swapped roles every minute or less.
As late as 1901 there was double-jack team that was confident that it could beat any steam drill in a fifteen-minute contest. These contests used granite, usually from a quarry in Gunnison, CO, which was chosen because it was believed to be both very uniform and very hard. At one time around 1900, the record for a double-jack team was 55 in (in 15 min). That is nearly 4 in/min! I believe that they were right. This champion team *could* have beaten any steam drill in a 15-min contest using Gunnison granite.
How do we translate this to an 8-hour shift of a single steel driver with his shaker? I wish I knew. Should a single steel driver be able to do 50%, 25%, or 10% of what a top Western double-jack team could do in 15 min? I don't have any real idea.
What I do know is that there were exceptional individuals who did amazing things. There is a record of a single-jacker drilling 31 ft in very hard rock in an 8-hour shift. This rate is 68% of that of the world champion single-jacker, drilling for just 15 min.
If John Henry could have driven at 68% of the rate of the world champion double-jackers in Western contests, he would have drilled 147 ft in 8 hr! What he actually did, according to C. C. Spencer, was 27.5 ft, 0.69 in/min, about 19% of the rate of the world champion Western double-jack team. To me, this seems quite realistic.
Spencer says that the steam drill made only 21 ft. For 8 hr of drilling, this is only 0.525 in/min, only slightly better than the reported average for a double-jacking steel driver under ordinary working conditions in hard rock. If the drill were actually working for half of the 8-hr period, this would be reasonable. If it had been working full time, it probably would have made about 40 ft in 8 hr (1 in/min).
Thus, the steam drill would probably have won if there had been no mechanical problems. With significant mechanical problems, John Henry could have won.
It is sometimes argued that John Henry's contest could not have occurred as late as 1887-88 (when the RR in Alabama was under construction) because by then steam drills, which were tested extensively just after the Civil War at Hoosac Tunnel (MA), would have been perfected to the extent that no human steel driver could win a contest.
This argument is nonsense. It overlooks the fact that there was no improvement in speed between 1870 and 1887 - the improvements were in reliability. It also overlooks the fact that even in 1887 no steam drill was perfectly reliable. It was not uncommon for the drill steel to break or for fitchering (stuck steel due to an angled hole) to occur.
There is a contemporary record (21st or late 20th century) of an operator of a power drill being killed by being impaled by a ricocheting broken-off steel.
Fitchering was certainly still a problem in the late 1880s. The recommended procedure for releasing a stuck steel was to hammer on it sideways. If it came unstuck, then the operator had to try to redrill the hole to straighten it out. When this didn't work, the hole had to be abandoned.
John Henry's opponent had to deal with all of these potential problems, broken steels, nonlinear holes, and stuck steels.