Thanks everyone for the great input.
On the PRR with domes, I have a set of MTH O27 streamliners (plastic, not aluminum) and they look great behind my semi-scale WBB GG1, a poor-man's re-creation of the Congressional set. MTH provides a dome car, so I'm OK with violating aspects of reality since I'm not a pure scale guy. I just don't like mixing road names on passenger trains and see Lionel (or Luxury) Lines as sort of a wildcard that can run with anything, but not if there's Santa Fe markings on the.
I do, however, try to stay true to some history. Semi-scale PRR runs with O27 Madisons, for example, not freight.
I should've pointed out that my NYC streamlined Hudson is the semi-scale ESE. Right now, I'm running it with red lettered WBB O27 streamliners (plus my grandfather's Lionel Clifton dome car). The cars look a little small to me but I don't want another set of MTH O27 streamliners (which are a bit bigger) in NYC since they're a direct copy of the PRR's. I think this would be a good opportunity to go a little bigger, like 15", since I have 42" and 54" curves on 3 of my 5 mainlines.
Think I'll wait around for some 15" K-Line NYCs that went with the ESE. They're really hard to find other than at an astronomical price. There's a set of 15" Williams NYC aluminum streamliners on the auction site that have me interested as well.