I don't think 18 would have pulled that train up the hill unassisted. We were a good 50 tons over tonnage. I would have tried 10 tons over but not 50.
The track speed through the S-curves - and in fact the entire RR from Alamosa to Sierra - is 30 mph. I ease off to 25 for the curves as those top-heavy dome cars don't like to hit the curves that hard. There is no chance of them going over, but the ride is not very good, in my opinion. And I am my own worst critic.
The S curves are part of the original narrow gauge alignment. It would have been easy to straight line all of them, but I guess it was not a priority to the Grande.
With our normal 4 car train 18 easily rolls along at 30 mph with lots of power to spare, but with this train, it was all 18 could do to make 25.