Malkoffs are solid as the OP has noted but are not noted for maximum outputs at minimum cost.
One of the best things about the Malkoff series is that they are one of the few high-end P60's that still perform well with CR123 primaries. Many of the other dropins out there have eschewed CR123 compatibility to get higher outputs, making many of them lithium-ion specific. I don't know if this is a consideration for the OP but I like having at least one of my high-end lights compatible with CR123's in an emergency, if need be.
This is a GREAT point that I was going to need to address before purchasing anything anyway, so I am glad it was brought up. Here's the situation: I have the 6P, which I hope to have bored out to fit an 18650 since I have other lights which already use those (Fenix TK30 & TK35). The other light is supposedly a Surefire, but I haven't gotten a positive I.D. on it even after contacting Surefire; it looks like a 6Z, but it is plastic. The battery chamber has a metal sleeve that I am unsure if I should remove and, therefore, don't know if it is a good idea to adapt this one to 18650 (although I am open to suggestions on this topic). To sum it up, I have one light that I hope to mod to fit 18650 and another that seems as though it may remain CR123 (at least for now).
I will have to look into how to tell which light engines will work with which batteries...
As for usage: The plastic 6Z fits on a rail mount so I will probably use it for home defense when the zombie apocalypse happens, but until then it is either going to be a general purpose light, or I may get an infrared drop-in for photo purposes.
The 6P is what I would prefer to carry when I shoot photos, both for light painting as well as a defense measure if approached.
My objective for both/either of these lights is to upgrade to a light that is at LEAST as bright as the current incandescent bulbs they have as well as sporting a much longer run time per battery/charge.
I will look into all of these suggestions, which I appreciate.