If you already have 18650 cells and charger I would look at some of te newer 26650 lights.. They put out 200-400 more lumens than the smaller 501 models. The great thing about the 26650's lights is that they come with a tube so you can use your current 18650 cells while you decide whether or not to move up to the bigger 26650 batteries.

the single cell models work fine in lockblocks and the extra output is very noticeable. If and when you move to 26650 cells you can expect 2+ hours of full power output.

http://www.ebay.com/sch/i.html?_nkw=...&_osacat=16037