Forget it. RTFE, irrespective of type, is no longer reliable beyond 232 C (450 F). Some people claim some resistance to 260 C (500 F) but there is very little data to support valve seats made of RTFE at that temperature. Generally, if you need sustained service between 232 and 315 C you must use PEEK.
If you're just using a design temperature of 232 C and service temperature will be 200 C or below, you will be OK- but the pressure rating of the valve with respect to temperature will depend on its construction. You need the chart offered by the manufacturer, and then to ask the manufacturer what testing or standard they base that graph upon.