I did some testing upon DPC Latency issues, seems there is something with Avast NDIS Firewall Filter Driver.
Done with a Killer Xeno Pro, all tests are done by watching some videos on youtube.
6.0.0.0 with the NDIS driver enabled, my first impression was that the Killer driver must be the cause.
http://img411.imageshack.us/img411/4025/bf60.jpg
So I tested a few drivers trough, and then it hit me to try disabling the NDIS driver all together.
6.0.0.0 with the NDIS driver disabled.
http://img109.imageshack.us/img109/7752/noavast.jpg
EDIT: To make sure I tried to remove AVAST and test with COMODO.
6.0.0.0 with COMODO’s NDIS driver enabled.
http://img686.imageshack.us/img686/5306/comodoi.jpg
Tool used: http://www.resplendence.com/latencymon
NOTE: This is with the older 6.0.0.0 Xeno driver, the most recent release makes it look even worse for AVAST.