User blog comment:Tekkphreke/Shikai and Bankai/@comment-4207271-20131224061221/@comment-4207271-20131224083602

Wasn't it more like "in general, by learning Bankai, one's power can grow 5 to 10 times greater"? (Taken from her wiki) This implies that there are cases that exceed the stated power increase or are below it.