The 800's could possibly have done 120 mph with a passenger train but they would not have come even close to that number with a freight train, even if the freight cars had been equipped with passenger trucks.
Aerodynamic drag would prevent it from happening. Passenger cars have diaphrams which reduce the drag on each car, but every freight car will be producing front end drag and rear end parasitic drag. Plus, with 40 ft. freight cars, there are two sets of car ends for every one on the passenger, never mind the diaphrams.
I once saw an empty coal train on a South American line (RFIRT) that was almost halted by strong head winds. The 2-10-2 on the point simply could not overcome the effect of 60 mph winds blowing into 40 - 50 empty coal gons. Granted, gons and hoppers are a worst case, but even PFE reefers would produce a lot more drag than a passenger car.
So, what is the fastest recorded freight run in the USA? In the world?