I have several MP-15's and S-2's, all w/ dual motors. They can pull a decent sized consist. I have a small layout so the most I usually run is 4-5 027 passenger coaches, or 6-10 freight.
All of my engines have been wired in series to slow them down. I've also added weight to them. The front trucks tend to jump the tracks on tight curves.
IMHO they will pull much bigger loads.