Bullzeyebill
Flashaholic
ITN: I've seen a few L4Ds around and read a brief tutorial on how to make one. I don't know if the lens falls out or not, but it was not mentioned. I'm not that great with the flashlight math yet, but I don't doubt your equations. I think my KL4 is an overachiever and I'd be glad to get 25 minutes out of one rcr123.
If you can measure the current at the tailcap using an RCR123, or 17670 you can get a fairly good idea of runtime. The closer the figure is to 1 amp the better. I just checked mine and it is pulling 1.16 amps with an RCR123, and 17670 with both charged up at 4.15+. SilverFox has tested RCR123's and finds that you are getting closer to 500mAh at 1 amp or so with a really good high discharge RCR123 like the Powerizer.
Bill