Oh, sorry - I was a bit too quick there :)
I meant DPC latency, please check with this tool:
http://www.thesycon.de/deu/latency_check.shtml It will probably show about 1000us - which is normal since win8 is not compatible with it yet. If you have a
stable 1000us it probably is fine.
Then you can check the latency with this tool:
http://www.resplendence.com/latencymon This shows the latency caused by which process, drivers and programs :)
For instance, my Nvidia driver and FW driver was causing too much latency for me (in Win8)
For you it could be completely different.