Efficiency is the name of the game and these new Cree's are only marginally more efficient (180 versus 176 lm/w). The biggest difference is their ability to take 33% more current so to utilise these gains, a driver swap will be required along with a corresponding drop in runtime.
Plenty of flashlights out there can do 1k lumens for 5 hours. My 5 year old Thrunite TN35 can do that with 3 3400mah batteries. I've got a soft spot for 4D Mags, so I'm looking forward to a runtime test for this one,
Normal chemistry D batteries are terrible at providing sustainable high current. A nominal 15Ah battery will be significantly less at 2A current draw. If Maglite have managed to get a solid 5 hours at 1000 lumens I'll be in the queue for one! ;)
I've got the M2R and it's got a great flashlight but.... I'd like to see the UI changed slightly. When using the momentary tail switch I'd prefer the flashlight return to previous state. For example, if you had it on a low lumens from the side switch a press on the tail switch would boost the...
Generally, most USB charged flashlights have electronic switches, and so there will always be some battery drain. However it's usually a miniscule amount and doesn't need a frequent top up charge. Research your intended purchase for standby drain or ask here.
For those scenarios I'd consider the Olight R50. It's a compact 26650 based flashlight so runtimes are long (50hrs-50lumens) with huge output only a double click away. The only real downside for me is that the lowest output is 50lumens!
The problem with C cells is that they can't produce a lot of current. They're good for small current over a long time but not the reverse. I'd guestimate a 2C would be limited to around 500 lumens. The exception to that would be Ni-mh cells, if you were thinking of those then the option for high...