The Quicktime upgrade is giving some problems . Details here http://www.info.apple.com/kbnum/n93414 , but it's a long shot (not really a connection issue)

Looks like you tried everything else. I had a similar problem with uploads, and it turned out even the ISP's help desk wasn't informed that filesharing was being throttled.

Have you tried connecting directly (bypassing the router) to see if that makes a difference?