Around how many freight cars can a GP7 realistically pull?

[nachoman]

Modeling I would say 12 cars should look about right-less for roller coster layouts..For terminal work I would pulled no more then 15 cars since 15 cars looks like a long train on most home layouts.

That's a good point. Few of us have home layouts large enough to handle more than 12-15 cars, which should be well within the range of a GP-7. I've never worried about my locomotives out pulling their prototype, because I have never had a layout large enough to have such long trains