Lots of info on the lights in my comparison thread. It covers numbers, beamshots, and who is brighter at what battery state among other things..
I have not written much about my subjective "long term" owner thoughts, but ill probably get to it. In short I prefer the K40M and think its the better value light for any flashoholic who have an 18650 charger. If you have an X40 and like the tint and dont need a super smooth beam, no need to buy the K40M. X40 have several advantages too (size, step-less dimming, battery light, built in charger, throw when freshly charged, you feel where high mode is, etc). When it comes to it, which is better is subjective, there are small advantages that goes in favor to each light.