The refresh rate of your monitor does not limit the framerate at which your games run.
It just won't display fast enough to let you see all 80 frames that the graphics card is drawing.
This is the scenario where you can either increase the graphics quality of the game to get no visible loss in performance (average), or you can set a framelimit (at 60) so the graphics card won't go to the extra effort of drawing frames that your monitor can't display.