Braff:
I'm currently running a gopro6. most of the clips I've posted here were done on a gopro5. the first videos I published here with a 6 was the Bentonville stuff.
the jump from 5 to 6 is significant. in terms of pixels, I reckon not much. physically, the removal of the enclosure for making the camera itself waterproof is hit-or-miss. opening the various panels to access the SD card, battery, and charging port is a lot more difficult on the 6, especially on th trail. on the plus side, not having the constant rattling of the plastic outer enclosure means you get nice stereo sound quality. for example, on the BCGB video, towards the end, you can hear my heartbeat, as well as the wind coming from different directions when I turn to cross the creek.
the game changer is the internal stabilization. user interface is different (I won't say better), but with the 6, they finally got some MEMS tech to auto-flip the camera. however the 6 is more buggy than the 5. that auto-flip could be more reliable; but any halfway-decent editing software should allow you to flip the video in case it is recorded upside down. also, the one-touch feature (hit only the shutter to power on and start recording, vs pressing the power button first) has a tendancy to lock up the camera, requiring a hard reboot (popping it open and pulling the battery).
all in all, I'm very happy with the 6. the stab is just amazing. not having to spend extra the money on a gimbal for about the same price as the whole camera, and not having that extra chunk of hardware hanging off my chest makes it totally worth it. with the 5, I had to tie a knot in the chesty to get the elastic tight enough to not bounce the video into unwatchability.
WARNING: if you get a 6 and want extra batteries, get the gopro brand. the Fuel spare battery I got at Best Buy (had the coupons, so fuckit) fits, but just barely. closing the door is VERY difficult.
I think @KuЯdt has a 7 or 8. I can't speak to whether the bugs in the 6 that I mentioned above have been addressed in either of those models. I got the 6 because I read the res and stab were reportedly not noticeably better in the 7. none of the additional features present in the 7 were anything I cared about.