I am doing a 4GB download from Georgia tech right now. I have NetMeter running and watching the download speed it is all over the place. Not even a V pattern like you are seeing.
It bounces randomly something like 28,24,16,33,35,16,18,28,etc.. Even dying a times for second or two. Even the download spped showing on Firefox's downloads window is all over the place.
See attached graph for how bad it is... Cannot even tell if powerboost is even there or not.