Do you only have 3 choices in Stockport?
Because, if so, make sure that the school you put third is a banker, ie one you will definitely be allocated should you not get AGSB or SGS. You don't want to risk missing out on all three because then you would be allocated a place at whatever school is left that still has places, after everyone else has been allocated their choices. By definition, that's not going to be a school you want.
Of course, if you get more than 3 choices then you have more flexibility and you can ignore me