Hey Herc driver!
Like your work, the "Swift" car is my favorite, followed by the 1st box car in the 2nd set of photos.
I guess my 2 comments are these: 1) on those cars that you used a "faded" type weathering, from what I usually see on real box cars, dark areas fade much faster and more drastically than light areas. It is not a consistent all over fade. For example: I recall seeing a photo of one of the white Guilford box cars with the black and orange "G" and reporting numbers/paint. Of course the white did not look faded, but the dark G and reporting marks were faded and chipped and rubbed in certain places. Also, with the fading, the seperatley painted name and reporting marks chip away a bit.
2) comment is: I wouldn't worry too much about over-weathering. While we all tend to like the nice clean cars we buy at the LHS, here in South Florida, and as I recall from my days in the northeast, freight cars are a mess. Almost every day I see the local box cars CSX uses and they are covered in grafitti, dirt, dust, often very hard to see reporting marks and railroad names or logos are obliterated. They are EASILY as dirty as your most extreme car. Intermodal spine cars from TTX? can't see a spot of yellow on them, its as if they were painted brown; the only clean boxes are the newer ones, and even a fair amount of those have been grafitti tagged. I saw a shiny new CP Rail 60' excess height box with the nice beaver logo, entire bottom of the car was covered in grafitti.
Most of the places these freight cars are going and sitting are a mess, weeds in the tracks, broken fences, rail debris, garbage. Weather hits em' too, look at photos of CP Rail red diesels in the winter, they are a dirty, brown mess. Constant Florida sun fades the blue paint on FEC engines (whose "white cab roofs" are usually more of a graphite gray due to dirt), and turns red Ortner hoppers more- orange. And older cars? I have a NS video and the old "southern serves the south box cars"? They are missing most of the letters!
I like where you're going with your weathering. All the things people say about using india ink or chalks are true, they work!
What can I say, I'm a dirt fan!
all my best!