Those Constants didn't work for me, when I print them out, it only says 0.0 or 1.0, But when I use:
Hmm, now that is odd, they work here. Another mystery! Guess I will have to start using the other method again maybe this one is somehow CPU specific. (Edit - they seem to work fine here on Intel (Win 2004) and AMD (Win 98) processors ??).
Anyway pleased to hear you may have found the source of the problem and it is not specifically related to the Gforce. As you say if they had disabled the wait for Vsync this will override Flip true and it will probably give some massive FPS when there is not much to be rendered.