Thanks for the encouraging comments!
As Paul has discovered the Blue Comet loco uses tbumptex only, though having had an opportunity to explore it all deeper since, I have found that you can get slightly better surface definition using tbumpenv as long as there is good definition in the normal map.
Personally I prefer this over tbumpgloss because it reflects the moving clouds and sun and it reacts slightly better when the subject is poorly lit. Used too heavily it will drastically change the original surface color. Used gently it has subtle advantages over straight tbumptex to my eyes.
I have made a more comprehensive post in Content Creation so as not to bore innocent onlookers.
http://forums.auran.com/trainz/showthread.php?t=61731&referrerid=74
As Paul mentioned, 25 materials sounds excessive but for something consisting of so many seperate parts it's not gratuitous. There are 2 main textures for the loco body then 12 for the alphanumbers. There's a small environment map for the glass, a seperate texture for the coupler to make it quicker to share between models and a small seperate texture required by the script for the works numbers.
Add to that the normal maps and we're up to 18 there already even though all the body mapping essentially comes from 2 textures. So yes, it's true that excessive material use isn't recommended, I wouldn't say that in this case it is avoidably excessive. Probably using 2 x 2048's is the most extravagant thing I did, but the goal here of course was to create a premium model with a good sales lifespan.
As Paul also noticed the normal maps are only half the size of the diffuse. I made this decision considering I had used 2 x 2048s already. Of course it's perfectly ok to do that if you don't need the resolution, it's not like using a seperate opacity map where the size must match that of the diffuse texture; I think they do need to have the same aspect ratio however.
Cheers and I hope you enjoy the set for some time to come!
~R~