I wear a size 13 Salomon F22 (pretty damn small footprint) and ride a 259mm waist with no problems. And i'm a freeride/carving guy. I've seen people with clunkier size 11 boots that are bigger than my F22 13s
Depending on how wide your stance is and what board it is you may be able to stuff 13s on a board with 25.3. I have 13s and have fit on boards with waist widths that small. Personally, I prefer 25.7-26.1 and avoid widths bigger than that.