I just bought a 15m cat 6 cable and the connection to my desktop is slow 2-4Mbps.
I have a Netgear DG834 router with the latest firmware that's reporting a 19Mbps connection speed. My wireless speeds are good and if connect the laptop to it wired I get rocking speeds. My desktop is a fast machine with a new Win7 x64 build.
Can the cable have such a big influence on the speeds or is there something I'm missing?