Thanks to Dick's suggestion, I've recently had Virtual Railfan running while working on other things on the computer, and it's amazing on how long the trains have gotten. One in Tucson was 3 locomotives, two more mid-train, and I counted 277 cars. All double-stacks.
While I wouldn't expect anybody to model a train that long, it did remind me of some conversations we've had over train length over the years. The gist is usually that once a model train gets to about 20 cars or more, it "feels" longer. We've got evidence that local freights in my era could be 20 cars fairly regularly, and on many models that's a through freight.
Not all of the trains I'm seeing are that long of course, but there are a few other factors that I think come into play when trying to determine how long of a train on the model is "good enough."
Watching the Videos
That's a 30 car train and definitely wasn't the maximum that the FAs could handle up the helix, so I think once I get the decoders in those locomotives I'll test a 50 car train and see how that looks going through the center of town.