insulating around firebox

Now I have searched and i have narrowed it down but the 2 products im looking at are mineral wool and kero wool the mineral wool has a heating rating of 1200 degrees and the kero wool has a heat rating of 2400 degrees obviously the mineral wool is cheaper and I can get it really cheap through a buddy but what I dont know is will I see temps that high in the fb? Its not going to be directly at the flame but between 11ga and 16ga steel. Any input would be greatly appreciated thanks