The PW GG1 at 14 1/2" inches is noticeably different in detail and design. Compared to the 19-1/2" scale version you will see that the the PW version simply feels - short. Now in an environment of smaller radius trains, this wouldn't be much of an issue, but put it next to any of the scale Railking offerings of MTH or Atlas Trainman line equipment, the size issue does become relevant.
As to detail, there was not a lot of detail on these locomotives to start, and that was by design, these were representative of pre-war modernism in every sense of the word. Imagine that in the mid 30's you had you UP M10000 and the Budd self propelled Zephyrs, but this locomotive showed that you could have modern grace and brute force combined in a single package. The main thing to note is that the entire PW GG1 will only come up to past the second set of windows on a scale version.
The result is the proportions get compressed quite a bit. However the locomotive is the same width and height as the scale version. I think the main details a PW version will lack are things like the detailed pilot, the extra detailing on the pantographs, refinement in the trucks and running gear, and the prototypical numbers. GG1s were numbered 4800-4838 with 4800 being a riveted prototype that is a seperate class unto its own in a way. The 2332, 2360 numbers from the pw era were typical of not applying prototype numbers to trains at the time.
As to the running qualities, they are both fine runners, its really just a function of your interests. Since I grew up around the real thing and rode a few trains pulled by GG1s, they have always been in the 80' range to me. I could not get used to a shorter version. But that's just me. If your pw versions suits your needs than perfect.
Not side, by side, but:
