I'm by no means a techie, but I had similar issues and found someone here on the tech support boards suggesting to disable LargeSendOffload for your ethernet adapter. Seemed to help some for me, making the spiky periods less frequent. Of course could be unrelated, but it's easy to try. Googling that and it seems to be a common culprit with excessive latency. You can find instructions here in the thread with !FIX! something in the header or google if it's no longer here.

Also just now tried one of those routing services for a free 30 days - that did actually help me quite a bit, going from very laggy and spiky to a seamless 120 ms post installing. I do however live in europe, and I suppose the benefits for me would be more helpful.