I briefly tested P3P video modes 4096×2160, 3840×2160 and 1920×1080 (footage at ground, imported to Final Cut Pro 10.2.3 and output to 1920x1080 H.264 10Mb/s. I evaluated images exported from video in Photoshop).
The only difference between 4096×2160 and 3840×2160 is that the latter is 256...