I was hoping that someone could advise their experience with the pulling power of the 1:20.3 forney locomotives?  For example, can they pull a similar number of cars as a 2 truck shay?

I am stuck with some pretty steep grades (6%), and am ok with short trains, but I want to be able to run at least 4-5 cars in a train.  I really want to get a forney, but I can't afford to buy one just to test it out.

Any help would be greatly appreciated!