Specific to the Bachmann 9F, my four specimens have been galloping around the layout for 15 years now, pulling trains of up to 2.5kg, and keep in mind I operate daily if possible. Still run equally smoothly compared to the brass bearing models I use. I reckon that the light plastic compatible greases now available do the job of wear reduction much better than the oil of the past, when significant wear was observable in mazak chassis block axle holes.
Until we can persuade more manufacturers to take up the 0.6mm flange depth that Heljan have been using, we are stuck with the need for compromise when wheels are closely spaced, to enable the flanges of adjacent wheelsets to clear. Bachmann opted for equidistant axle spacing on their 9F, the compromise an extra 0.5mm, so a 2mm overlength coupled wheelbase. I have yet to read a single complaint about this, let alone a review that picked this up; but what is evident is equidistant axle spacing as on the prototype, a better compromise in my opinion.