What about driving the p7? Can a single 17670 or 18650 adequately drive these LEDs? I have a 3 led (P4) Peak First Responder that chews up and destroys low quality RCR 123s and cannot run at full power (around 3amps, I believe) on an 18650. Best config for that light is a pair of 18500. Even my single Q5 MRV digital needs more than a single 18650 to fully power itself.
With a 2.7 amp draw (is that full power on the P7?), I think a decent, reasonably priced drop-in is going to take some thinking about power sources.