Turbodog,
The L4 will get hot. Especially running on a Pila and just letting it sit there. The L4 does put out a lot of light, but if you run your KL4 on Pilas exclusively and get tired of all of that heat and are willing to sacrifice some of that flood for lots more throw, then...
You can modify it. Taking it apart isn't hard. Once you have the head apart, just unsolder the 5W emitter and slap a 3W emitter on it. You'll get just about as much light (just in a different form. More throw, less spill), a lot less heat, and almost twice the runtime.
With the KL4 in this form, you could run it on the 2 cell body with the Pila or a single cell body with a single 123. DO NOT run it on 2X123 cause you'll smoke it.