I don't think it's a zero sum game and I'm pretty sure other factors are involved e.g. stress, alcohol intake, volume of exercise, etc). I do know that my perceived quality of life is improved when I'm getting plenty of sleep, and for me that requires about eight hours.

As I wrote in my initial comment the occasional disturbed night is not a big problem when I'm well rested. Under those circumstances I never feel the need to get extra sleep to compensate for the lost hours.