you mean waist width 250mm and boot size 11. That is exactly my setup, I have a Rome Agent 154 with a waist width of 250mm and my boots are Burton size 11. I just got done test riding that setup for 3 days and to be honest if you center your stance perfectly in the board, were there is exactly the same amount hanging in the front of the board and the back, you will not have a problem. In the 3 days of riding I really never saw myself hitting the snow with either the front or the back of the boots. You might have a problem if you plan to carve at extreme angles, but I did not nave a problem carving at normal angles. My advice is to try it out and see how it feels, but I would not worry about it.