So toyed around with the 16fps silent mode but i was always getting corrupted purple frames. When I turned off the force 25 fps mode though the fps dropped to 14 and I wasn't getting any purple frames.
I decided to test record time in this 14fps silent mode. My resolution was 1736x3256. I was using the card that I benchmarked on reply #4211 in 192MHz overcloc k- Sandisk256GB 95MB/s. I went through the various bitrate settings (10-14) with two exposure scenarios, one as overexposed as possible, and one only a little overexposed. I also had global draw turned off in the video submenu, and sound was disabled. Once a clip hit a minute I called it continuous and stopped recording.
Here is an imgur album of six screen caps of different examples (3 for overexposed and 3 ETTR)
https://imgur.com/a/W62ZSyxIt seems my card's in the field write speeds taps out at roughly 68-70MB/s. This new build is pretty stellar. Thanks Danne!