Lots depends on where the probe is tapped. On a 7.3, drivers side manifold just past last cylinder and before up pipe is thought to be the hottest place..
You can run 1250 max continuous and occasional burst for less than a minute to 1300 or higher.. there’s plenty of ford guys hauling at 1250 running up to 1400(I’d be sweating) on a short hill climb but the aim is to run it as cool as you can. With a stock engine and driveline you shouldn’t get into trouble. It’s when you start rehearing , power adding, turbo swapping , etc that this comes into the most play