With the help of nick crisp I got the is 17 see here http://foc-u.co.uk/index.php/topic,12268.0.html
Recently picked up a schuberth s2, very happy with it. HelmetCity had them down to £350. Though Infinitely had a few down to £280 this weekend. Only down side with the s2 is my glasses steam up due to too much padding around neck.