Same problem, things slow down as soon as they hit the cogent network.
StardockCorporation.demarc.cogentco.com is the boundary point where anything after that point is Stardock equipment. Think of it as the property line. Everything to one side belongs to us, everything on the other side is Cogent/someone else.
We are working on being less dependent on a single provider for our connectivity. It's just a bit of a slow process (I was out in another datacenter on Friday for this problem)