Update...I got the 960 LD41 and compared it to my older 680 LD41 last night. There are some minor changes on the newer model. Very minor in my view.
The grip pattern on the body is a little different, the lens/mirror head outside is ever so slightly different, and the tail end is a shade longer and narrower than the older model. The wobbly tail standing feature is the same. It still stands up, though. No difference with that.
Looking at the mirror itself with the LED at the bottom, both models look the same. No differences in shape, angle, led placement or anything like that. The cooling fins on the outside have been moved downward about 1/8 inch. That's the only thing I could see. And the electronics changed inside to give the output differences.
The battery cradle is the same inside.
Now the important stuff. I took both lights outside at night and compared them. First off...No difference in cone pattern that I could tell. The light color looked the same, too. No donuts or hot spots. Really good patterns. What I would call a fine beam from a flashlight. Looks like day on high power.
There are of course differences in the brightness settings. I am telling it like it is and my honest opinion. I used only my eyeballs and a dark night against trees and buildings. On the lowest power setting you could tell the difference. I do like the lower lumen level of the 2015 model better than the older model. 6 vs 10. Bumping up to the second and third positions, you could see the differences. But not much. On the highest setting, I could see a difference between 960 and 680 lumens. But not much, either. I shined the lights at objects from my back yard and across a pond over 300 yards away at a tree line for the highest light level. The 960 lumen looked to be about 10% brighter. No difference in beam shape, color or any of that. I am sure our own eyes also compensate for differences we do not notice, also. Just like a camera sees things differently than when you look with your own eyes.
The bottom line. The LD41 is a wonderful light and top quality. Fenix quality is the best. However, if you are price conscious and do not have an LD41 yet, I would say, "Get the older model 680, before they sell out". $77 verses $49. $49 is a heck of a good deal for that light. If you have a 680 model and want another...get another 680 before they sell out for that price. There is not that big of a difference in my eyeballs between the newer and the older model at high power. I do not think I would have noticed any difference had I not used both lights simultaneously to compare. One was just a shade dimmer than the other on high at a distance. 10% difference maybe. If you want to know you have the brightest, then buy the 2015. I learned that on the upper end of the lumen scale above that 680 line, 300 lumens more does not make that big of a difference. To make the difference, the beam pattern would have to change. And I like the beam the way it is on the LD41. I also lean the way Bill, (WJV) mentioned...the 680 model has better spacing of lumens giving better run times. This lumen race lately is all about sales.
