I have an Imperial SD70, a BNSF with PS2 from the BNSF Husky Stack RTR set released in November 2010. I had some issues with the paint coming off but it was taken care of by MTH, at no cost to be despite being way out of warranty. It is very close to scale. I think the Imperial version is full scale except in length. I think, off hand, the RK is 2 inches or less shorter than the Premier.
I also have the following Imperial Steamers...
* Imperial Pennsylvania K4 4-6-2
* Imperial Pennsylvania USRA 0-6-0
* Imperial Norfolk & Western Y6B 2-8-8-2.
I will be ordering the new, soon to be released B&O B6 0-6-0 with PS3, which should be showing up in the next few weeks.
I try to buy all Imperial products now. Excellent products and detail for low costs.