I'm 5'10, and I sit fine in a 16 inch...the 17 inches doesn't make a difference. I actually always thought it was a 16in, until I saw a 17 stamped on it...oops.
It didn't fit my horse basically because he's shaped like a balloon. Freakishly wide & round backed. Honestly, he never offered a buck or showed any signs of pain, I could just tell it was too small. It really should fit the average QH though...Rudy's just "special needs". Took forever to find a saddle for him...grr.