Can't really put a figure on how much boots will pack out.... Generally speaking a size or maybe even two sizes can be expected...
Each boot is different as far as sizing goes. I wear a 14 normally and 14 Vans Cirros were a bit snug when I got them right... Well they've over packed slightly in my right boot so I had to buy tongue eliminators from tognar.
My advice is if they're hurting you that bad you should go up a half size buddy... If anything you can wear thicker socks or get pads from tognar if they do over pack slightly.
"When I do good, I feel good; when I do bad, I feel bad. Thatís my religion." - Abraham Lincoln
Moral of the story: If your going to rob people, wear a diaper.