You’re quite right!
It makes very good sense of Cree to subdivide the bin boxes at the lower Kelvin temperatures.
The perception of the color shift between two temperatures is not proportional to the Kelvin temperature but to the reciprocal temperature. See the MIRED scale here.
So perceptionwise the 1A box is quite small and the 5C1 box is quite big.
Scaru (or anyone else that knows) - I've been trying to figure this out, but simply can't do it:
From a CREE part #, can you tell if it's exactly 1A, 1C, 3A, 3C, etc.? The part #'s in question are XM-L2's:
XMLBWT-00-0000-0000U20E1, XMLBWT-02-0000-000LT60E3.
What I can tell:
XMLBWT-00-0000-0000U20E1 - 6500K, 65 CRI (on mouser.com)
XMLBWT-02-0000-000LT60E3 - 5000K, 75 CRI (on mouser.com)
The E1 and E3 are kits #'s, where E1 includes 1A, 1B, 1C and 1D, and E3 includes 3A, 3B, 3C and 3D (all from the CREE data sheet: CREE Xlamp Xm-l LEDS). So if the kit #'s can't point you to the exact tint, what would? Or do you simply have to take your chances?
Ohh! Forgot to mention: Thank You scaru!! This post is very informative!!
I think those are "order codes" and you might need the "bin codes". Page 2 of the XML Binning & Labeling guide shows the difference.
To see an example of a Cree "bin code" in real life, check out the package in this photo.
Ok, yes i saw those too but that info doesn't seem to be provided by Mouser. Those order codes are called the manufacturer part # by Mouser, so, still unknown what you are ordering?
Sadly, I think that is true. One can get a general idea from the bin, but nothing conclusive. E.g. it is a U2 you know it is CW.
That could be worth a shot.
Turns out he deleted the comment after I hit the quote button. ;)
Lol Scaru, I think that post of mine was up for all of 30 seconds.
Here is my revised response:
Some sellers know the bin code and will tell you if you ask. If the sales rep doesn't have that info handy, someone in the warehouse should know. If they sell individual stars, the bin code is usually printed on the back of the star. If they sell by the reel, the bin code is usually printed on the reel.
Having said that, I've never tried calling Mouser, so I don't know if that's something they would do. Same goes for Digikey.
Sorry. :P
I got 3 of the XM-L2 T6's, installed one today in a C8 pill - not too bad, similar to a 3C tint. But definitely would prefer the U2's, and now the U2's are showing in stock and the T6's are out of stock. The XML2 T6 seems to work ok, even though I originally put it in backwards - duhh, wish it was brighter though. Wonder if I did some damage - in theory I should be getting 3.77A but measuring only 3.6A. The U3 1C still seems to be brighter on a simple ceiling bounce test - the U3 1C is 3.8A bu design and measures 3.8A exactly. So, I should order a few XML2 U2's but for $7.37 plus shipping, not a great deal. I'm thinkin I may destroy some of the stars when removing them, so may need some blank stars but can't locate any, not even aluminum, forget about copper...
Hhhmmm, may be off topic here with that info.... Still Mouser and Digikey are the two main sources to get the CREE LEDs bare, and you can't tell what tint you are buying? Weird...
They list the tint - ie 3000K, 4000K, 5000K. Just not the tint bin - ie 7A vs 7B, 5A vs 5C, 3D vs 3C, etc.
My limited general understanding of this subject is that daylight is broad spectrum light but LEDs are binned based on the dominant wavelength and also has other peaks as well as missing wavelengths. Does hi-cri mean that the led has a better broad spectrum output(fewer gaps) with the penalty being lower overall output?
Thanks! 
Yes, it contains a much broader spectrum. If you look at the spectrum of the Nichia 219 (H1) it is much broader than the one of a XP-G. (See Below)
As you can tell, the Nichia 219 is superior in that way. Also one can see why the 2600k XP-G is higher CRI than the 5000k XP-G.
talking to Craig Shih from Illumination Supply about it and he said it’s just a roll of the die which tint you’ll get within a given kit no. One of the downsides of ordering bare LEDs from Mouser/ Digikey. Still, from what I’ve heard, all of the 3* tints are pretty nice.
Great information here! Thanks a lot for compiling and sharing it. Sticky’d.
+1
Thanks Scaru.
I bought 2 of this type from mouser, they are out. The do have the XM-L2 U2 6000K CW:
http://ca.mouser.com/Search/ProductDetail.aspx?qs=5YqktSXERipfLuRE%252bJbsug%3D%3D
Links to U3? At least I found some before.
XM-L2s are very rare and hard to get 
U3 or equivalent or better XM-L2 neutral white anywhere?
Illuminationsupply has some XM-L2s.
Relative noobie but digging deeply, it has come to my attention that the CRI of any light is commonly misquoted. The typical way of measuring CRI in the first place is comparative, and there’s simply not a standard. Did you know, for example, that a single candle has a CRI of 100? So it’s a good point to consider that the emitter bin tint of choice is going to be compared to a “true” value of it’s primary output and given a CRI rating to match. The LED is usually low in the CRI comparison here because of what’s already been said…it has a narrow spectrum.
I’m a photographer, looking for the tint bin that will best suit photography purposes in the 5700Kelvin range, and the CRI quest got me confused! I’m sure there are those here that understand it far better than I, but the reading I’ve done lately points to having to consider ALL the pertinent data, not just a bin code or CRI factor.
So, anyone know the proper XM-L or XM-L2 to assist in photography? Of course I’d like colors to be as accurate as possible, but I don’t think I’ll be using a candle for macro photography!
Thanks for any help and all corrections
I made a little visual overview of LEDs on 16mm base from fasttech. Double checked with others and their prices seem to be the best…
Personally, I really like warm white at this point, 7B/7C tints… They are like incandescent lights… I think they are just as awesome indoors as outdoors. Everyone who has seen my T3 7B vs regular T6 (1A?) prefer the warm classic light. Colors and everything just look better in my opinion. Ill might try something on the more neutral side soon…
Not a fan of cool blue. Especially if the beam have some “green-ish” or purple looking tint…