I have also recently lost the ability to stream HD Netflix. Have not tried off peak, but during evening hours iPad, Apple TV and laptop all seem limited to SD. Additionally I now have a 10-20 min buffer time when trying to stream HD movies form iTunes all of my AppleTVs. Previously movies would start before displaying a buffering message.
Internet service is Comcast 105/20
Speedtest.net shows 69/22 to laptop over wifi to regional server and 50/7 to distant server.
Seems suspicion that performance of both services drops around the same time.