We usually use the train for the purpose of getting to another land later in the day, when we still want to do rides, but just use it as one of our "breaks".
As poster above said if you have plans on riding Dumbo and Peter Pan, head there FIRST!! We tried this for the first time last trip, what a world of difference.
We got Fast Passes for Peter Pan, headed to Dumbo, a 10 minute wait. Then did IASW next, then to Peter Pan. We didn't even need the FP's. When we got off, we handed them over to others.