I checked mine and the 18650's only provided a slight uptick in illumination. You should still consider upgrading to 18650 because of the larger pool of bright lights available with those cells..
best bang for the buck 18650 lights are, priced lowest to highest.. The new S mini could easily be used as a helmet light, since it is so light..
http://www.shiningbeam.com/servlet/t...4-II-R5/Detail
http://www.shiningbeam.com/servlet/t...-rocket/Detail
http://www.shiningbeam.com/servlet/t...P-dsh-G/Detail