To answer Airman00's question about what an S-2 will pull: plenty! Almost thirty years ago, I was a partner in one of the earliest contract switching operation. Our customer, a long-gone chemical plant, wanted their storage yard re-arranged, putting all of the old friction bearing and out-of-test-date tank cars at the far ends of the storage tracks. The cars were an assortment of MTs and loads, 55 and 90 ton, friction and roller bearings.
We took turns running the engine, over one Saturday and Sunday, and I distinctly remember asking the guys in the ground how many cars I had on the nose of the RS-1 we had at the time. It was upwards of sixty! True, we weren't going very fast, due to track conditions and handling hazmats, but the old girl didnt really breathe hard, either. Just slow and steady-
I know Airman asked about the S-2, but an RS-1 has the same mechanicals and electricals, just on a stretched frame to accomodate a boiler and the road trucks, so the comparison is valid (OK, so the RS-1 is typically five tons heavier-)
Something to remember here is a very basic rule of thumb, perhaps over-simplified: Weight produces tractive effort, needed to get a train moving, while horsepower provides the acceleration, once the train is moving. The Tazewell example is impressive, but within reason, any other switcher could have moved that train, if the unit was of equal weight, and the motors could have been kept out of the red. The RS-1 I used to run could have pulled that train, but granted the SW-1500 would have accelerated it faster.