I've said it once, I'm going to say it again:
l4d/CS/whatever, are not "benchmarks" that you should even be comparing to. Go find a canadian server, on the east coast, that hosts 500+ people on it, and find one that uses iweb as their ISP.
If you want to find out who the culprit is, you should do a traceroute on the server, and find out where exactly your ISP is saying fuck you to Anthem's ISP. Because I know that Talis had some issues with a west coast server (test server) due to some University of Connecticut or some crap that the ISP kept trying to route through.
Other things to keep in mind: Mouse freedom sometimes plays a part in why people lag. ie: find that mouse freedom dll and delete it.