I'm having a similar problem with download speeds varying between 2-10Mbps on my 200Mbps connection. Second line tech support couldn't see any util. issues in the area and noted it was at 50% at the time. Which part of the country are you in? Out of curiosity, when you run a speedtest.net to the local VM node in your city, do you get full speed?
The Speed during off peek is usual not an issue and I can get good single thread and Multi thread speeds. Anywhere between 60Mbits and 100Mbits or so single thread. Usually always my full 150Mbit multi. During Peek times it plummets and I can't stream anything but low quality with 2Mbits speeds if I'm lucky.
Netflix own speed test Netfilx Speed Test is currently giving me 50Mbits now it's past 12am and I can get 100Mbits or more during off peek at times but all evening it's been between 4 and 8 Mbits.