I have on in 2 rail. So I can't answer you curve questions. In 2 rail my smallest curve is 48 inch radius and it does not hesitate on it. The Weaver 0-8-0 would slow down or stall on that.
There is a chinese brand can motor, not a pittman. It is mounted with a closed gear box with gear reduction to allow the motor to use a better torque range which improves slow speed operation.
Mine will easily pull 15 or more cars on level track. My cars are free rolling mostly Atlas which are not lightweight
The detail is a little basic in terms of brass but very well made and as good as any diecast I have seen.
The B6sb represent the latest ones Pennsy built that came with power reverse and hense the smaller cab.