ISO auto on manual mode (M) on D800

I'm curious why you want to shoot at greater than 1/60s for video. High shutter speed on video will just make the video look choppier. 2X the framerate is a good rule of thumb for shutterspeed for smooth video. You don't usually want or need high shutter speeds in video as you aren't stopping motion, so if you have a reason you need to do it, I'd be very interested in hearing what it is for my own info. Thanks.