like people have said the only difference is the size of the liner. It really just depends on your comfort, whether you like a roomier boot or not. Always remember with a bigger size you can always bake it to make it fit better
as people already said, the shell is the same size, just a different liner.
It will def make a difference, but not a huge one, if that makes sense.
It depends on how much of a better deal it is IMO