Hi ulillillia, Ive read a couple of threads where you have described this
phenomenon, so I am somewhat familar.

I have v-sync turned off in my adapters settings, and I have the newest drivers.
Here are my results using the f11 Statistics Panel;

fps_max = 60; //32 fps (under 63
fps_max = 64; //63 fps
fps_max = 200; //63 fps
fps_max = 300; //63 - 152 fps? very erratic
fps_max = 400; //142 - 242 fps? very erratic
fps_max = 500; //507 fps
fps_max = 600; //~352 fps? erratic
fps_max = 700; // and higher give ~576 fps? erratic

Strange!

The manual says the range is 10 - 400 default 240.
at the default 240, I get the cycling I described above
and ~63 fps. If I set the max to 64 however, I still get
63 fps but the cycling disappears. As a matter of fact,
around 64 is the only place I can set it that gives a steady
fps.

I get a different result though when I use my own fps calculator
that averages frames. The fps stays at 64 when fps_max is 64 or 400!