I would expect some efficiency gains from not having to carry a diesel generator with you, and some efficiency gains from not needing to design it to fit on a train (my understanding is that bigger generators tend to be more efficient).
There are also efficiency gains from being able to run the generators continuously, which justifies spending more on them. Combined-cycle gas turbines are more efficient than big diesel engines, and their fuel is cheaper.
I would expect some efficiency gains from not having to carry a diesel generator with you, and some efficiency gains from not needing to design it to fit on a train (my understanding is that bigger generators tend to be more efficient).
There are also efficiency gains from being able to run the generators continuously, which justifies spending more on them. Combined-cycle gas turbines are more efficient than big diesel engines, and their fuel is cheaper.