P.S. I am thinking of switching to a hybrid system where xxxSwapInterval(1) is called once per N frames (I think, 5 or 10) while the rest of the time the loop tries to adhere to the timing using micro-sleeps (hello, TimeBeginPeriod(1), you ugly freak) and can measure SwapBuffers()+glFinish() duration freely, thus getting real results not contaminated with v-sync wait times.