The Weaver/CMP car is a model of a different prototype than the Atlas OSB car. I think it is a newer prototype built for a number of Western roads. There was an extensive article on prototype in Railroad Model Craftsman magazine in the 90s. I compared the car models I had with drawings and they worked out pretty well.
Atlas cars are models of the USRA prototype, designed and mostly built around 1920 when the Government took control for the RRs late in WWI and proposed all new equipment to a group of Standard Designs specified by the United States Railroad Administration (USRA). The USRA developed designs for many steam engines and many freight cars including boxcars, hoppers, and gondolas. I don't know if they got into passenger cars or not.
So the Weaver/CMP car can be a nice variant that is supposed to be different than the USRA cars.
I think the MTH OSB car is also a USRA model. I don't know much about the Lionel and MTH products. I have seen a few MTH and they appear to be the same as Atlas
I didn't know Pecos River (John Smith) ever did any woodside cars in plastic. I have seen lots and lots of the 50 ft boxcars in plastic.
As for all looking the same, that idea does apply to the bodies, but I think in terms of paint and even lettering, it might be more prototypical to mix as long as you stay within the era you model. Older paint schemes can always be seen in later times, but newer ones should not be. Also, paint fades and peels and what not and older paints in the steam era were not as good as newer ones, so they faded and wore faster. So different shades of the same color are probably more prototypical in a train. The various cars would have been built and/or painted at different times and hence faded differently. Also where they traveled might cause more or less paint damage.
