Background information: I own 2 Fenix P3Ds. I also just received 6 L2Ds in the mail, most of which I'm going to give out as Christmas presents to hopefully turn some people into flashaholics (see www.candlepowerforums.net for definition). Both of these lights have their positive and negative aspects. I think the L2D is better as a general use light, or for a person who doesn't know what they're going to be using the light for. The P3D is a bit more of a specialized light, and may not be the right choice in many circumstances.

I think alot of people failed to notice the light in this specific thread is going to be used as a helmet light for a maximum of 20-30 minutes at a time. In this case the P3D is clearly the best choice for maximum light output with minimum weight and size (when runtime is not an issue).

Using an L2D instead of a P3D would simply add size and weight, and slightly decrease light output, for extra runtime and a more common battery which is unnecessary in this case.

Here's a quick comparison shot of the 2 lights/battery types: