I’m not sure if there is a similar review for the 3V XHP50.2, output should be about the same as the 6V version(Testing a Cree XHP50.2 J4 3A led) at half the current, so 2200lm at 5A, without counting reflector losses. The improvement won’t be much. There is no way that a XHP50.2 can make 2000lm OTF at 2.8A and 3-4.2V, that’s about 200 lm/W, only obtained when underdriven.