Not flicker but tucker^^

If the Code looks like this:

Graphics 800,600
bglsetswapinterval(0) '<--- return 0

while not keydown(KEY_ESCAPE)
If MilliSecs()-timer>1000
timer=MilliSecs()
fps_=fps
fps=0
endif
fps:+1

SetColor 255,255,255
DrawText fps_,0,0
flip
wend

...DrawText return about 47-50 fps, display is running@115Hz. What should i do to achieve more than just 50fps -_- ?