I guess compatibility is my top priority, but not necessarily P60 compatibility, if that makes sense. If there is something small(er) in the Surefire line that will allow me to beef up its output (total lumens or possibly even just throw) or try out different options (emitters, engines, heads, etc.) then I'm game. I've come to this desire by way of my disenchantment with Surefire's output-to-co$t ratio and a growing fondness of tinkering.
I love the looks of the E1L but am unimpressed with its output. If the adaptions you and Donn mentioned will jack it up yet keep it small, I will be leaning that way.
I'd suggest a visit to the store to handle the lights, if you can. You can't get a full appreciation for their characteristics without hands-on time.
The E1L has, by current CPF standards, relatively low output - but it does it for quite a long time. The E1B is fairly bright based on rated output, but the simple number we focus on is deceptive. The optics used in the E1B provide a tightly focused beam that is surprisingly effective.
A few general observations about modifying these lights...
Any of these lights can be modified or lego'd with other components. If you're working within a relatively modest budget for doing so, the 6P has lots of inexpensive, yet decent, stuff available for it. There's less available for the E series lights, and if you're buying commercially, there's less in the budget category, so expect to spend a bit more if you're staying in the E world.
You can, as previously mentioned, use an E body and a C head to try and get the best of both worlds - that's why I included the FB-1/2/3, and especially the FB-3 mated with an adapter and standard Surefire C series head, in the photo. You may or may not find the result attractive.
Don't obsess too much about getting the "perfect" light. You'll always be able to sell, gift or relegate a light to a different role. You'll also probably find that your criteria for satisfaction will change over time.
- Syncytial.