[Noggo]

I would ask admin to move your post to "Internet Services" section. I dont think its a home network problem. I would advise you to test without your router in place though (PC connected direct to cable modem).

I take it your getting spikes in latency all the time, with peak times a lot worse than off-peak (if so join the club).

Unsure whats going on with your modem logs, but I'm sure it shouldn't look like that. Have you been in touch with tech support. Newsgroup support is by far the quickest way to check the logs / signal levels out.
Just post description of what happening + modem signals + modem logs on:

virginmedia.support.broadband.cable

(if tech staff asks you to do ping or trace route tests, you'll have to do them with your router removed just to save you time in re-posting info, if you go down that route).