It rather depends where you are on the list. I think the admissions registrar is usually very helpful about where you are and your chances. The deadline for acceptance is not till Wednesday, but I am sure there will be some movement then. I know quite a few boys who are turning down their places. Good luck
I would have thought your chances are very good at 11. In my eldest son's year number 15 on the waiting list got in easily, but it was 3 years ago and I think there were double offers still that year for Sutton and Tiffins. I know 4 who have said they are not taking their places and possibly one other, although I know at least one of them have struggled with the decision between Sutton and an independent and may not actually decline the place for a little while as they have nothing to lose. Not at all fair, but the place will become available in the end. People are still playing their cards close to their chest.
My son gave up his place- (he's going to Wilson's) and I know of 2 others from his school who are also giving up their places. So that's 3 down.
Good luck!