Extruder temperature limits

I have a gmax 1.5+ with dual jhead extruders. I am concerned about overheating the extruders. Can you tell me what maximum temperature I can safely use with these. Thanks.
In case others have this same question, I asked support this question and in a couple of days got back an answer. "The Jhead hotend is made of PEEK plastic so the max safe temperature is about 243C."