Does anyone know what would cause my download speed to be in bursts like this?
http://i.imgur.com/XDry6sD.png
Steam stops downloading if the disk that it is writing to becomes busy (usually if the OS is doing an operation).
It could be various other things, such as other people on your network, some tom foolery occurring with the local WAN or even just the server you are downloading from doing some weird form of round robin download....
But seeing as the download appears to stop, I'd say it is steam stopping due to disk access.
Thanks for reply, do you know of a way to keep the disk from becoming busy?
Start download and walk away.