This answer your question its not the biggest loco in trainz.
There are 2 SD80E-2 & The Goliath both on DLS and scrapped projects, The Goliath was never tested and derailed on swichs. No one bothers making these because there no point in them they are hard to drive ans slow down plus there a pain to turn on craves its like driving a ship on sand.
The Goliath would be the larges in trainz don't bother trying to dive it on any O route its to bigboys back to back more less. The project is in the Trainz graveyard.