The width of the horse has to do with it than height. I'm 5'9 with long legs and I am very comfortable on a 13.3 h stocky haflinger. However, I've also ridden 15-16 hand TWHs that felt too small because of how narrow they were. My legs were hanging well past their bellies.
The other thing is what you plant to compete in and at what level. Cutting and reining horses its not uncommon to see a grown man on a 14 hand horse, while higher level of dressage they want to see small people on HUGE horses - or at least that is what it seems like to get a specific "look" between horse and rider. On the trails - who cares what you look like as long as you and the horse are comforatable.