hi, i can't decide between a shoei small or medium helmet. i went to the shop today and tried on helmets for 2 hours. i decided that the arai and shoeis were the most comfortable for my head. agv was loose around the sides of the top of my head and they didn't have shark in a small. my head is 57cm. both brands specify small as 55-56cm, and medium as 57-58cm. after 20mins the small felt a little tight on the top of my forehead and back of my head. the medium was comfortable. the small felt as if it could potentially give me a headache after a long time, though it wasn't unbearable. i'm worried if i get the medium.. once it loosens up it will be too loose (i am already at the bottom end of the medium). will the small loosen up enough to be comfortable, even though i am already 1cm too big judging by their specs? i am going to try them all on again but am looking for any guidance as to how much the small will actually expand. thanks.