EagleTac G25C2 XM-L U2 or Xm-L T6 Neutral

I am looking at buying the EagleTac G25C2. I do not understand the difference between XM-L U2 and XM-L T6 Neutral. I understand the neutral part, but wat else?

I will use this outdoors for camping, hiking, walling trails, etc.

There is no difference between the to as far I know. Just the U2 is brighter, and will illuminate more then the neutral white at when you are camping. The neutral white just mimics more of natural sunlight and makes the outdoor scenery more natural instead of the whitish blue.

U2 and T6 refer to different XM-L "bins". After production, LEDs are tested and classified into different bins according to chromaticity (color) and luminous flux (brightness).

U2 is the brightest bin, but is only available in cool-white tints.
T6 is the next brightest bin (7% less output) and is available cool-white and neutral tints.

Hence U2 is preferred for maximum brightness cool-white output while T6 is preferred for maximum brightness neutral output.

You can read all about XM-L binning here.

Neutral tints are often preferred for outdoorsy use as they have a more pleasing color rendering on foliage. Personally I prefer neutral tints, but there is no shortage of differing opinions on the matter.

Some interesting beam shots in the forest. They don't directly compare the U2 vs T6, but they compare the T6 neutral with similar powered cool white lights. The neutral white does seem to show more detail in the forest, not just more accurate colors. Notice the trees in the distance and you can make out more trees in the far end of the road, than you can with similar powered cool white lights. Again, not a direct comparison of the G25c2 U2 vs G25c2 T6, but I think it does a good job of showing how well the neutral tint works out in the forest: http://www.youtube.com/watch?v=2QOLjDWVsts