Rogers cable is horribly inconsistent. Advertised 30mbps down/10mbps up. Yes, 30. Not 3. Numerous tech visits/calls and no fix. St. John's, Newfoundland
I was having similar problems and it was an issue with one of the PCs on my LAN that was slowing down all of my network traffic. I rebooted that PC and all was fine.
I would suggest that you shut everything down on your LAN including cable modem, router, switches, WAPs, all PCs, Xbox, Wii, iPad, phones, etc.
Then power up your cable modem, then your router and then boot up one PC. Run the speedtests with only those devices. Then start adding back everything else and see what happens.
I have the same 30down/10up package and I have a question.. Have you ever gotten the full 10mbps upload speed?. I've never seen mine go past 3-4mbps. Bunch of calls and conversations with tech support led me nowhere.