From what I've read (on TrainzDev), new content will take use of new features, including normal maps. Older content will supposedly work, but will not look as good as most of the newer content...
As for the NZ content. If you can find 3rd party people willing to build high quality NZ content with the new features enabled, then you might be lucky. However, much of the new content will be made by 3rd party groups.
Oh yeah, if you look carefully those 3 are very different. They are similar but then again a lot of UK locos look the same to me...
Zec