I use the hero3 black as my FPV cam and after a fair bit of use I have ended up pretty much sticking with 1440p30 as my FPV feed. Main reason is the extra vertical FOV so when flying more aggressive in ATTI or GPS modes I can still see above and below me. In the 16:9 modes even in the widest FOV settings this lack of vertical FOV makes it very hard to either set the camera at an angle where I can see ahead when pitched heavily nose down and also see below me when level.
Also my vtx transmits in 4:3 SD and so the gopro is also outputting in 4:3 mode so if using a 16:9 video mode I get less veritcal image on the screen. I also have now set my screen to 4:3 input where I had it at 16:9 before, in 4:3 mode I dont use the full screen as it gets the black bars on the side but the image isnt squashed. Using 16:9 fills my screen but no matter what video mode it stretches the image horizontally to fill the screen. This makes it very hard to see altitude and seeing as I am shooting in 1440p30 this will fill the screen vertically anyway. Shooting in any 16:9 mode the output from the gopro is still in 4:3 so it gets black bars top and bottom which are filled with the gopro OSD but I am losing image space and if set to 16:9 in the monitor it also gets distorted making the altitude very hard to judge.
Here is a screen grab of a video I shot with my 3d setup when accidently using 1440p30 on one cam and 2.7k30 on the other. The 1440p30 is full frame here in the background and the 2.7k30 scaled to match and shows the difference in FOV both vertical and horizontal.
I think the image is cropped but here is a link to the full 1920x1440p jpeg
http://imageshack.us/a/img38/6537/2v9g.jpg
Also my vtx transmits in 4:3 SD and so the gopro is also outputting in 4:3 mode so if using a 16:9 video mode I get less veritcal image on the screen. I also have now set my screen to 4:3 input where I had it at 16:9 before, in 4:3 mode I dont use the full screen as it gets the black bars on the side but the image isnt squashed. Using 16:9 fills my screen but no matter what video mode it stretches the image horizontally to fill the screen. This makes it very hard to see altitude and seeing as I am shooting in 1440p30 this will fill the screen vertically anyway. Shooting in any 16:9 mode the output from the gopro is still in 4:3 so it gets black bars top and bottom which are filled with the gopro OSD but I am losing image space and if set to 16:9 in the monitor it also gets distorted making the altitude very hard to judge.
Here is a screen grab of a video I shot with my 3d setup when accidently using 1440p30 on one cam and 2.7k30 on the other. The 1440p30 is full frame here in the background and the 2.7k30 scaled to match and shows the difference in FOV both vertical and horizontal.

I think the image is cropped but here is a link to the full 1920x1440p jpeg
http://imageshack.us/a/img38/6537/2v9g.jpg