Hi there, I am new to Bachmann HO trains, I would like to ask what is the difference between, a GP40 listed here for $45.00, code 63501. It just says 8 wheel drive, and a GP35 listed for $53.00 code 11517, it says  8 wheel drive 5 pole skew wound motor. Does the Gp35 just have a better motor or something.