Hey macjet,
I have one of the new SD40-2's..It is one of the new RTR units. Although I have never owned any of the other SD40-2's releases Athearn has offered, I have seen them. Although mine is undecorated, my friend bought the Milwaukee Road Bicentennial unit. The details are stunning IMHO. The paint is better than the previous releases, grab irons are now installed, as are fuel tank details (plumbing) and the windows are flush as well. As with the last release before these newest ones, the handrails are plastic and look better. The horns and prototypical details are there on the select models that would have had them (ATSF SD40-2's have the cab mounted AC) However, there is still no tread on the walkway, no MU hoses, etc. I prefer it like this anyways as I like to add my own details. I think they look better and they are pretty cheap as well. Detailswest makes some REALLY nice brass steps and walkways that are pretty easy to install. As you may also know, they make just about every detail part to bring it up to levels exceeding the other big companies any day. I'm not sure if there is something specific you wanted to know...Also, I'm sorry that I can't tell you too much about Rock Island prototypes either. I would recommend one of these to anyone though. I have some "alright" pics I could post of my undec unit if you need to see a specific angle or something. Hope that helps!
-Rich