To GeoBruin: Yes - All are welcome to chime in - I think it's great to hear and learn from experiences of others - Guessing we'll have a few posts on this one - and I'm looking forward to reading all of them. I've already heard of two lights that I'm looking into for potential purchase.
To LEDAd1ct: Question can be applied in either format. A light that meets ALL criteria would be great, or as roadkill1109 answered in preference to each specifically.
To MT7: Not speaking for roadkill1109, but I've also read in a few locations that the M3X out-throws the T40CS by a tiny bit. As for lights, I too am looking at both of these for a purchase, but am leaning towards the T40CS for the UI. In my opinion, The T40CS is a true one-handed operated light with the side switch and has 3 brightness settings plus strobe. The lowest setting can run for a stated 60hr run time which for me can be useful in situations where I need to conserve battery power. The M3X requires to twist the head between high, low and strobe - and although I like the option of reducing it's size with the 3X CR123 option, I'm still leaning toward the T40CS for my needs. I'm also keeping my eyes open for the Klarus XT30(?) which has not been released yet, but is stated to be their thrower version of the XT 20. It will have one larger head as opposed to two smaller heads. Guessing overall lumens will be less, but throw should be better. I love the Klarus UI set up with both buttons in the tail cap, but don't own any Klarus lights as of yet.
Cheers,
RC