I was designing a triple P7 or MC-E Mag and then I found one made by Mac available. I've had it a week or so now and it is very very nice. The low is impressively low (D2DIM controller) and of course the high is amazing. This one has three AW C Li-Ion cells at 3300 mAH, so it should have a bit over an hour runtime at full power and lots more dialed down to lower levels. It has been shortened to about 2.5D M@g length. I especially like the dimmable feature and memory so you can select the amount of light required for the job and get that level each time.
I also have a single P7 and an MC-E light, and for just about anything they are enough (and a great deal more portable). A single 18650 cell driving a quad die led with some kind of dimming control (like the new D2Flex) is just about ideal for most uses. There are some DX lights and the Wolf Eyes Sniper that have several levels. (Single level P7/MC-E lights are too bright and get too hot in my experience.) These are far more available and cost effective (than a triple) and the difference between one P7 and 3 P7's is not required for most purposes. Also, a triple P7 or MC-E head will overheat at full power in almost any reasonably sized light if run for very long, especially if your hand is not providing liquid transfer cooling. 36 watts of LED really need fan cooling for continuous use. That's more power than most small soldering pencils. Even a single P7 in a Mag at full power gets hot after awhile. Many if not most P7 flashlights today run at less than full power and heat is one of the reasons. Of course a P7 or MCE run at less than full current still produces a lot of light and the efficiency is higher, so you get a lot of lumens per watt!
I have been very tempted to put together a P7 with D2Flex in a 1D M@g and set it up to power it with any of: triple AA nimh carrier, D LiIon, 18650, C Li-Ion. It would be a very short light with plenty of output for most uses and with a lot of power source flexibility. An extension tube 2D in length would even allow using 3D or 3C alkaline in an emergency. How's that for flexibility. (When the light is being cut down, have the original tube rethreaded to be the extension.) It is not too hard to put one of these together, there are folks on the forums selling the cut down M@gs, heatsinks, LEDs, battery carriers, etc.
I see that the single P7 lights from DX et al have come down in price, the MTE 5 mode that I have is quite reasonable for the price, now well under the $50 I paid some months ago. The Wolf Eyes sniper MC-E or P7 models are better made, with larger heads and more throw (but still plenty of flood). The WE has a forward clicky and a user interface that keeps the SOS and strobe out of the way, and it will also take a pair of CR123 for additional power flexibility when required.
Good luck in your quest,
-- Alan