Excellent idea, that's one diagnostic I hadn't tried. Switch 2 next to switch 1 worked fine.

I even re-capped the far end of the 200' run in case that was the problem. No change.

These test would seem to indicate that the 200' run is the problem. Well, technically the sum of these tests appear to indicate that nothing is a problem. When I'm plugged right into the end of that 200' run, everything is fine. When I attach a switch, everything slows down to a stop. When I attach the same switch to the first switch that that run is plugged into, everything's fine again.

Argh! I hate networking...