To maximize write speed/get maximum recording times for High resolutions on 5D3 (using Danne build):
-Cards:
CF: Sandisk Extreme PRO 160 MB/s UDMA7
SD: Sandisk Extreme PRO 170 MB/s UHS-I U3
-Settings:
-SD Overclock: 160 MHz
-Card Spanning ON (from RAW video submenu)
-10-bit lossless
-Use Frozen LV from RAW video submenu (instead of Framing preview; in broken/cropped preview presets)
-If the scene was static, after setting your scene and before hitting the recording button . . toggle the preview to Canon preview by pressing Info button (keep Frozen LV) to get rid of Global Draw and gain extra write speed.
I recorded around 1 Minutes and 52 Seconds in 3840x1536 1:1 @ 23.976 FPS in 10-bit lossless (I stopped the recording manually), I have exposed to the right in a sunny day . . pretty good recording time at this high resolution preset, I will make more tests in future.
-I calculated what was the write speed while recording that clip, it was around ~115 MB/s.