Dave,
I was the same as you when I first switched from HO to O. I thought these locomotives were all scale. Dave Minarick showed me the difference between the Imperial and Premier SD70ACe. The non scale reminds me of selective compression that we use all the time for structures, scenery, and even yards and sidings. I have no problem with it. Helps me run O trains in a small space.
Sleeping on it, I will hold off on the #40399 and give a look see on the RK and brass, I told the other guys I might do.
Thank you too for the advice!!