Most of modern flashlights control their temperature and regulate the power accordingly to not exceed the set border temperature. Smart.
So the simple deduction is the less heat gives the LED at certain brightness the higher lumen it can sustain. So the two indicators I’d focus on are: temperature gain vs power and lumen output vs power.
I want to build a flashlight for my night bicycle rides which can sustain the highest brightness. I don’t care of power consumption. Nor cri or tint. But it needs to be 5050 or less.
XHP70.2 and 70.3 have very good efficiency. Sustained lumens are also affected by factors including thermal path, flashlight thermal mass and heat shedding design, LED driver, temperature control firmware/sensor.
Kaidomain have a good selection of XHP50 and XHP70 LEDs. I’ve bought a couple of 5000k/5700k high CRI ones (XHP50.3HI and XHP70.3HI) off them recently. Just be aware the screw holes in their LED boards may not match up with whatever you’re planning on fitting them in. I discovered that last night with one of their hosts. Guess I’ll be relying on the reflector to hold the LED in place.