Kevin; Stephen put in real good words. Altho a steam locomotive is a relatively simple machine,
there are a lot of things that have to be taken
into conssideration in their design. Counterbalancing being one of those things.
And your Dad is right, the IC "One Spot" was slippery at high speeds and utterly destroyed several miles of track near Champaign, Il.
Your estimate of the speeds on the NG is right
on the mark. We paced some of the engines between Alamosa and Antonito where the 3 rail ran parallel to the highway and 30 to 35 mph was about tops.
A mechanical engineer friend of mine calculated the counterbalances for the IC. Would you believe that when they weighed the engines to determine the load on each wheel, that the weight of the engineer and fireman and the water jugs and ice in the cooler were included in the figures !
With something as massive as a steam locomotive
it is suprising to discover that even those small amounts af weight enter into the calculations.
Hang in there Kevin, it's a great and interesting hobby.
Jim