i read that a 26 cm waist-width is recommended for a size 10.5+. a normal width banana is at 25,5, so wouldn't have been enough, according to what i read. i'd rather have too wide than too slim
Very generally speaking, 26cm waist width is too wide for size 10.5 feet. Bigger boots will not make much (if any) difference at all - you effectively pressure/flex the board with your feet, not the boots.
It is a common misperception that too little overhang is preferable to too much. The opposite is the case for for pretty much everybody but the most hardcore Eurocarver.