If you are going stock, I say the K40M is a winner. If you like to mod, I would suggest the Crelant 7G10 (this link is from a quick search. Don't know the vendor). It's got a slightly bigger diameter head, holds one more cell, and is not a magnetic control ring controlled. I personally consider magnetic control rings a con as they limit driver options. It's slightly lighter than the K40M until you load with 4 cells. They are fairly cheap because they are so under driven stock.
Here is a mod that is way more then is needed with regards to the emitter mount/pill mod portion.
EDIT: In addition to mod effort, you would need to install a new driver to make the light really perform.
EDIT2: Forgot. Also very nice machine work, anodizing, AR coated lens, and stainless steel bezel.