Hello, im from Argentina (GMT-3 South America). I play Icecrown realm. Somtimes out of nowhere, i start getting latency issues. It varies, but generally more than 800ms. My PC is the only one connected to the router by cable. I dont have this performance issue in any other game nor application. My interenet is very fast and stable. Can you confirm if there are problems on the server? Maybe a region specific issue?
Warmane works just fine, so does your internet. Problem lies somewhere between two functioning points. You could contact your ISP and see what's wrong. There are also bunch of internet troubleshooting guides if you wish to try to fix it yourself, IP renews, DNS flush, router reset etc.