I've tried everything I've seen listed, I've re-downloaded my profile twice and I'm still getting poor performance out of my wired connection. I'm on cable and before the update my service was flawless. I had everything wired and running through a Buffalo WZR-HP-G300NH flashed with DD-wrt. I had a static IP on the xbox and set up QoS to almost always prioritize traffic to/from that IP address. Because of the service issues I was getting with the xbox and some unrelated problems with wireless, I changed the Buffalo router to a wireless access point and ran all of my wired connections (including the xbox) through an old linksys wrt-54g router (also flashed with dd-wrt and set up for QoS). My computers are working fine, whether wired or wireless, whether through the gateway router or the access point. I have end to end QoS and I'm still getting inconsistent service from XBL apps and games.
D: 126.96.36.199/ 188.8.131.52