That’s the peak temps inside the exhaust, obviously the materials are designed to contain, transfer and dissipate the heat so by the time it reaches the heat shield they should be far less. And under normal driving conditions where you also have the radiator fan extracting the heat and also some free air cooling, overall temps should be lower.
I couldn’t give you an accurate figure but I would say that the paint you’ve found is probably more than adequate. Just make sure your surface prep is good. Take some pics too, I might want to do this on mine.