George was a little under 5'6". According to the picture here (http://www.firstworldwar.com/photos/graphics/nw_nicholas_george_01.jpg), he was slightly shorter than his cousin, Tsar Nicholas II, who was 5'6", according to this site (http://www.worldwar1.com/biorczar.htm).
I'm not positive about the veracity of the Tsar source, but assuming it is true, then that's where I'd place George.