I suspect, and I've said this before, that the four hour runtime people are getting is due to the light not running in regulation anymore. As such, it will draw considerably less current and put out commensurately less light. I have yet to see the point of using a KL4 on an E1, guess if you got lucky and got a LED with a Vf of 5V (yeah, right /ubbthreads/images/graemlins/grin.gif), it might be worthwhile. But you are relying on something highly variable (Vf) as well as a light that is "battery" dependent. I just tried running two L4's I have on a single 123, one lights up fairly dim on Duracell, yet is fairly bright on Surefires. The other L4 doesn't light on the Duracell, and it's dim on Surefires. Pick another Duracell and it works well on the first light now. This Duracell has the same date code as the one that didn't fare too well (and yes, these are fresh, right off the package). Does this demonstration help illustrate my point? Probably off topic, so I'll get off my box.
Back on topic, the L4 is a pretty nifty light, especially when run off Li-Ion's which make it a lot more economical. Turn it on and forget it /ubbthreads/images/graemlins/grin.gif
CM