The video is exactly the same on both models because the 6+ doesn't use optical image stabilization on video, just digital.
And for photos the cameras are literally identical except for the OIS, which is only barely apparent in low light situations according to every comparison done that I've read. Looking at the pictures taken with both it's hard to deny.
Check this review: https://www.youtube.com/watch?v=PXBU9K6sQ7U#t=1288
Ois in low light does actually help quite a bit in cropping espcially, but other then low light and slightly smoother videos, same thing