Yes you will want to be careful with what some of the cheaper brands claim in sensor size and footage resolution.
The SJ6 also mention 4K but it is not the true honest to god 4K, and i think SJcams also acknowledge this.
But for trail running 1080p would be best with good EIS, and changing to photo mode to take full sensor resolution pictures is fast, and i think both the SJ8 and GIT2 also have time lapse photography, so you could leave it at that while running too, though i do think if you run in a shaded ares with low light there is a high chance pictures will suffer from motion blur.
Sjcams and GIT are also good at supporting their cameras, something that is hard to get with other low price brands.
I think the thieyet5e also are featured alongside the Sj6 in some camera comparison videos on youtube, but i cant remember how good its EIS is compared to the SJ6.
BTW SJcams also have a lower tier SJ6 without the front screen called Sjcam SJ6 legend air, other than the missing front screen and it use a 14 mpix sensor i think they are the same.
http://sjcamhd.com/sj6-legend-air/
http://sjcamhd.com/sjcam-sj6-legend/
Not sure how the two relate to each other on the prize, and if the air version have just as good EIS as the SJ6 legend.
I would assume chasing a 1080p frame around on a 14 mpix sensor Vs a 16 mpix sensor give a little more headroom for the 16 mpix sensor, but in real world use i am not sure i have not seen the 2 up against each other side by side.