The answer is pretty simple... You're not recording on the right card 20MB/s definitely sounds like an SD card speed.
You have to modify the default card to record to in your 5D menu (I don't have it right in front of me so I can't tell you exactly).
I've had the same issue this saturday and couldn't figure it out until I saww this menu
You have to modify the default card to record to in your 5D menu (I don't have it right in front of me so I can't tell you exactly).
I've had the same issue this saturday and couldn't figure it out until I saww this menu