CREE leds naming and what to choose?

Hello everyone! First of all I’m very sorry if there is already similar thread on blf but a cursory search gave no result.
Could please anybody explain meaning of letters and numbers in the middle of name of cree leds?
I know only that the last number is related to color temperature and thats it.

Look, right now I’m between XP-L Hi U4 8A (2700K CRI80) and XP-L HI T6 8D (2700K CRI90).
What all this letters mean - U4 or T6 or last A or last D in second cree?

And if i can ask in same place - is T6 8D (10 more cri) the best choice? Or it has any cons? Maybe very high cri generates more heat or smth else?
Thanks!
Updated: seems like U4 is way more efficient than T6 but I still do not know what last letter mean.

First two is flux and last two is chropacity (tint), check the datasheet page 17 to 24

That’s a very detailed datasheet. Especially since its just one LED. Its not even a circuit .