Unlikely to be of help, but i note anyway:
You are using QueryPerformanceCounter - what is the frequency you are given for it (btw, there is no need to re-query the frequency as it is strictly not allowed to change at runtime)?
That 65 sounds quite close to the 55 resolution limit (8253/8254 timer?). I have never seen GPC using that timer, but it is possible if your hardware can not give anything better (for example, my CPU has dynamic clock frequency and hence can not be used - instead some unknown much-much lower frequency timer is used [~3.5 mil, but high resolution]). I highly doubt you are suffering from bad GPC timer, but for sanity check you could do QPC in a loop and output the times (without frequency division of course) - to see what the resolution for your given frequency actually is.
edit: On second though - ignore that. Too bloody unlikely.