There is a reason we made a 5K camera.
The RED ONE was originally a 4K camera. With its Bayer pattern, it resolved 3.2K in a 4K package. Over 4 times the measured resolution of the best 1080P camera.
1080P is also a package size, not a measured resolution. The very best 1080P camera measures 1.7K of nervous resolution inside the 1080P package.
The reason we built a 5K camera is that it "fills up" a 4K package with resolution. Over 5 times the measured resolution of a 1080P camera and equivalent to IMAX that is processed in a 4K chain.
5K sensors have 60+% more pixels than a 4K camera. This is significant.
So when you compare 4K cameras... keep this in mind.
Additionally, there is a HUGE difference when extracting stills from motion.
We did not make EPIC 5K by accident.