Also tested here: https://budgetlightforum.com/t/-/48661, by Texas_Ace 
CREE states it's max output at 4.8 amps in 6V is 4292 lumens here: https://www.cree.com/led-components/products/xlamp-leds-arrays/xlamp-xhp70-2
If you notice, TA's tests show at 4.8 amps the output is very close to what CREE spec'ed.