Just some thoughts on possible causes without getting into running tests
If your playing wireless try playing wired to see if it is still the same.
Trend Micro AV for example has a known issue causing lag in games at present on Windows 8
Check to see if Hyper V is enabled to eliminate that as a cause, but seems more related to fps even though they say lag.
Although not related It is also worthwhile doing http://www.oscarcao.com/blog/2012/08...g-and-freezing
this restores the behavior to the same as Win 7