If I go to Org my NA ping goes from 125ms to 1580ms. My framerate drops to 10fps from 80fps and it takes 5 seconds for the flight master to respond to my click.
My computer is fine. My ISP is fine.
I have never had this issue, in a MUCH more crowded Org I might add.
This also happens in UC but to much lesser extent. FPS drops to 23 and ping goes to 500-600.
It's because there are a lot of players logged into ogrimmar. It used to be like this when there were a lot of players. That was almost 10 years ago, that's why you've never seen it before.
Orgrimmar appears to be fine for me. I have no increase in latency or drops in FPS, though that wouldn't be completely unexpected, given the rather large and concentrated population of the Horde on a single server.