There is a point where the additional bow pressure that results from extra righting moment due to the width starts to become a concern....like on the wide supercats (11' x 20'). The additional width gives it better speed potential but it makes them more sensitive to proper downwind handling...and more sensitive to sailing downwind in waves. However, you can control that by being wise with how much leverage you put on the bows...if you're in danger of stuffing it with the kite up, get your crew off the wire and start moving your weight inboard = problem solved. The trick is identifying that you need to do this BEFORE the boat takes you all the way to the scene of the crash. There really is not much concern with this change in the upwind attitude of the boat.

The 20 (at 8.5' wide) is one of the best ocean sailing cats I've ever been on. It will flat out eat waves and wind and you can sail with the confidence that as long as you can keep your weight rearward, the boat will not pitchpole (unless you're out in some REALLY crazy stuff). I think it would live and perform well at 10 or 10.5 feet but it's going to be less wave resistant.

Oh, and BTW, I've got a spare rear beam (standard width) from a 20 that I don't need.