The idea that a rock rating equals the hardest "move" is not very accurate. Over the years there have been many arguments for and against this proposition.
The YDS system cannot perfectly differentiate between moves and continuous climbing in the best of circumstances. Some examples from classic climbs:
Butterballs .11c: no .11 moves on the entire pitch. This pitch is given an .11 rating do to the continuous nature of the climbing.
http://mountainproject.com/v/california/yosemite_national_park/yosemite_valley/105936538
not too far away is
Waverly Wafer 5.10+ Consistent climbing not given a plus for its continuous nature.
http://mountainproject.com/v/california/yosemite_national_park/yosemite_valley/105992951
a bit more to the right is
Catchy 5.10+ a one move wonder way easier to lead than Waverly Wafer.
http://mountainproject.com/v/california/yosemite_national_park/yosemite_valley/105939236
Crescent Arch at the Meadows was explicitly given a harder rating than any single move do to its continuous nature.
Locally compare two classic .11bs.
ROTC .11b No .11 moves but continuous.
Saggitarius .11b with a very short .11b crux.
The routes I have been comparing have all been cracks on similar rock. Throw in different climmbing styles (edging, friction, steep ....) and rock types (limestone, rough, polished...) and ratings become even more confusing.
My guess is any high altitude 5.9 rating would be nearly meaningless. Well I guess it would mean hard.