Unless I were finally to jump all the way over to two rail (unlikely), I don't see myself needing any more. I've fixed pilots on three powered Atlas units, an unpowered unit and and "B" unit.
The Atlas model is very, nice--well done and one of their most detailed. The fuel tank is a little too large for the 60Ms, which carried a smaller tank to offset the heavier "M" cab. Otherwise it's a really well done model. The "B" units are eye catching in their own right.
The engine I'd really like to see Atlas run again is the ATSF Dash 8-40B. It was run once, in 2001, and oddly never again. A few camera grabs of the Atlas version:
RM