This is my HDMI test results on MLV with Audio enabled:
HDMI devices (Zacuto EVF & Atomos Ninja HDMI recorder)
With HDMI>Largest Frame size Continuous record,
1872x850 23.976p 2.20:1 with Audio 22,710/15:47 min 60GB 67.9MB/s buffer method 1
Crop Mode > 1856x938 23.976p with Audio 20,000 frames 68 MB/s buffer method 0
Tried the nightly build from Jan-1 MLV, and could get larger frame size continuous with HDMI
1856x930 23.976p 2:1 19,000 frames 55GB buffer method 1
Crash 2 times with hdmi plugin when I tried to record 1856x1004 and or 1872x1012, the buffer just filled up with blue color then lockup
Battery pull & reboot ok after that.
Any Sizes in the 1.85:1 or 16.9:1 are not possible in Large sizes more then 20 or 30 second clips
It seems on the 5D2 you are limited to about 70-73 MB/s without hdmi active
and with it active then that drops to about 65-68 MB/s & in crop mode to about 74MB/s
Its definitely usable without hdmi at this point, run & gun style with audio