I don’t have any firsthand experience with the latest Cree 5X5 form factor emitters. Do you prefer warm white or neutral? Which of the following 3 choices would you prefer, and why?
Neutral White - XM-L2 T4 5B1 (80CRI Min.)
Neutral White - XM-L2 T6 3C
Warm White - XM-L2 T3 6A1 (80CRI Min.)
I've had 3C and I currently have 5B1 and 4C. I prefer 4C. 3C was too cool for me and 5B1 reminds me of an incan.
http://intl-outdoor.com/noctigon-xm16-mcpcb-cree-xml2-t6-4c-led-p-755.html
Neutral White – XM-L2 T4 5B1 (80CRI Min.) - yellowish looking tint to my eyes - not bad but really doesnt look too neutral in my opinion… it is still nice as it has 80 cri
Neutral White – XM-L2 T6 3C - probably my go to tint for all my lights, only sacrifices 7% output vs u2 and is really just pure white light… maybe a hint of yellow in the hot spot/corona but otherwise great
Warm White – XM-L2 T3 6A1 (80CRI Min.) - very nice tint if you like incandescent like tint (think old maglite!)
3C is almost a little too warm for me.
I live for cool white tints; they just look so much brighter.
Someone mentioned before that yellowish/warm tints remind them of incan lights from long ago; I believe this probably has something to do with it.
Get all three and find out which you like the most! 
Tints are so subjective and based on personal taste it’s hard to recommend really.
3C, 4C and 5B1 are all nice fairly similar tints (all tend on the yellower/greener side of things) but with increasing warmth.
The 5B1 is a great tint if you like it’s relative warmth because it’s a tightly classified bin centered right smack on the Black Body emission line, so the chance of getting one that’s overly green is eliminated.
The 6A1 has more of a warm rosey/pink quality to it. Some like it some don’t.
If you're going to go with these low bins, I think you should also consider the S6, 7D3 90+ CRI. Lately I've found that it does a much better job of cutting through fog and making street signs legible than cooler tints with low CRI.
3C is great for me. I’ve really become a “tint snob” recently. As a matter of fact, I’ve always been extremely picky about the color of indoor CFL bulbs. But since the great guys here got together and sent me a boatload of fancy flashlights with neutral white tint, I’m now a convert and strongly prefer neutral white (around 3C) in all my new lights. The cooler tones just feel depressing and dingy to me, whereas the neutral white tone clearly renders the natural colors of things like rocks in the roadway and different types of vegetation.
I think the 3C is fairly neutral. In general it looks very creamy white to me, except I’ve had a few that were a bit yellow/green depending on the reflector. Color rendering is easily better than coolwhite but colors don’t pop.
I think the 5B1 is ideal. I would still consider it neutral, leaning on the warmer side. The color rendition is very good and makes the 3C look quite bland. The colors will pop more. The difference in CRI between a 5B1 vs 3C is similar to the difference between a 3C NW and some CWs I have.
Anything warmer than 5B1 I would (personally) define as true warm. 5B1 is borderline warm, especially when comparing with other tints. However, a 5B1 when used on its own still passes off as neutral enough IMO.
Even compared to the nichia219, the 5B1 does well in the coloring rendition. It just is a bit yellower/warmer.