I really don’t see how a D4 can sustain 600 lumens without active cooling. I just tested my D4 XP-L HI using my Texas_Ace lumen sphere calibrated with Maukka calibration lights and here are the results:
0s - 496 lm
4min - 256 lm
8min - 60 lm
12min - 31 lm
I’m not sure how Toykeeper calibrated her lumen measurement device but most lumen readings on BLF and manufacturer’s specs are much higher than ANSI certified lumens. Not sure if she got 600 lumen sustained under active cooling. I also did left it tail standing while waiting for the next measurement point instead of holding it throughout the test so it loses the heat sinking benefit from a human hand. The temperature of the light was pretty warm at each measurement interval. I doubt with a human hand holding it tightly will allow it to maintain anywhere near 600 lumens unless you set the allowable temperature to the max, which is not usable without gloves. Also these runtime measurements are normally conducted without a human hand holding the light. Almost everyone on BLF own a D4 so it can easily be confirmed. All you have to do is set the light to about 500 lumens calibrated with another light rated at 500 lumens (if you don’t have a measurement device) and leave it on the table. 10 minutes later, compare it with a 30 to 100 lumen flashlight and you will see how dim it is.
Regarding your concern about adding weight (210 vs 250 grams), I would say it would be pretty hard to tell which weighs heavier if you were given one light after another. Even if you were holding one in each hand, it is still not going to be immediately obvious. I just tested it comparing lights with similar differences. However, the performance advantage will be far more noticeable as I have described previously from my testing.