I'm also 5-11. I recently picked up a "small" 19" 1991 Attitude. I'd be better off on a 20" but when I mocked it up the fit is similar to my larger bikes bike from brodie and fat chance. It has rise on the mc1 like dareni's ride.
The measurements are weird. I think the 19" actually measures 18" centre to top. Correct me if I am wrong, but I think the easiest way to tell x-small and small MC1 Attitude apart is the water bottle mounts on the seat tube and cable guide. The x-small doesn't water bottle mounts and the rear cable brake guide wraps around the seatpost (the larger ones have a stop).