If you are flying a 5d you obviously have a nice gimbal to put it on which means that flying with the 5d as an FPV cam would be a BAD idea. You want to use a separate cam that is locked to the frame for orientation otherwise you would have no idea what the heli was doing. I know it's tempting as it would be nice to fly solo and see what the cam is seeing but you really need 2 monitors, a second pilot or fly LOS with a screen/partial goggles to do this.