I updated my Apple TV in november (shortly after Netflix introduced its SuperHD mode). For a long time after that, Netflix performance was abysmal (dropping down to sub 480p at times, especially during the night time).
I complained to netflix and verizon. The latter suggested I try connecting to netflix on a PC connected to the modem. I did and experienced no problems. No problems on my Android device or chromecast either. Only my Apple TV box had issues. Ultimately I found a thread on the forums which suggested a hard boot (power down) of the Apple TV device. Once I did that, the problems went away. If you have Verizon and use Apple TV to watch netflix, give it a shot.
I would love to see ars/netflix display a bandwidth graph by device.