The problem with excessive width to length ratio is pitchpoling. You drive the bow under and "wahooo", that is slow. If the guys settled in on 11 feet, I am pretty certain that is a good starting point. That is, unless you do as Simon suggested and also change the rig layout.
Tacking a 10 feet wide boat is not that bad if it is relatively light. Even better with a modern hullshape.