I agree with Gkitty. You’ve got an 8 dBmV drop in power from low freq to high freq, which is unusual to say the least and your upper freq Signal to Noise ratios are low. The upstream power level is a little elevated, within spec, but still a little above where it normally is. So, something is up, hopefully an easy fix. Maybe check the cable ends for the modem, at the wallplate and at the modem and ensure they are tight.
Can you confirm something for me? If you were to do a wireless speedtest with one of the other laptops when the desktop is plugged into the CGN3 and running, is there any effect on the wireless speeds at all? Just wondering if the port throttling issue has any bleed over effect on the wireless speeds. I haven’t heard of this happening, but with your laptops you should be able to confirm if there is, or isn’t any side effect on the wireless side as well.
You indicated that you had to go back to gateway mode to grab the DOCSIS WAN data. I'm assuming that bridged mode with a third party router is your normal mode of operation? If so, in that configuration, are you running into the same throttling issue when your router is plugged into the CGN3, ie a 10/100 Mb/s port on the router as well? There was another forum member who tested this in gateway and bridge mode and found that the throttling effect occurs both modes. What router are you using and do you happen to know if it has gigabit WAN and LAN ports?
Here is more food for thought. Your wireless performance will depend on your router, distance to router, house layout etc. and as well, the interference from other routers in your neighborhood. Here’s a link to inSSIDER, which you can load on a laptop to determine what other routers are nearby that might be causing interference for your router and laptops. This is the last freebie version available. It has since become a pay version that also supports 802.11ac.
http://www.techspot.com/downloads/5936-inssider.html
With that, you might be able to determine if its possible to find at least one useable channel with minimal interference on the 2.4 Ghz network, or you might decide that it’s time to switch to a 5 Ghz network. That has it’s own issues with lower range and penetration through house floors and walls, but, you might find that its interference free except for Terminal Doppler Weather Radar and other devices that employ dynamic frequency selection that operate in the 5 Ghz band.
The gigabit switch does work. I use one to connect all of the rooms in my home, and one of those connections is a Wii, which only has a 100 Mb/s ethernet / usb connection. Essentially it isolates the CGN3 from anything that runs at 100 Mb/s or below, and keeps the CGN3 and connected device running at their max interconnect rates.
Edit: added link for inSSIDer download