You're guessing wrong....
There's more than one PC, and they all have the same results with or without connecting directly to the Cisco modem itself or using a switch/router in between. 2 of them are HP proliant servers, proprietary enterprise class hardware with no changes. Video taken above was from a 3 day old windows 7 install on a x980 CPU w/SLI 580GTX, its not using no cheap realtek onboard NIC either. Even different cables have been tried and everything upgraded to cat6.
Speedtest.shaw.ca showing 220/13 at this time yet the YouTube still suffers.