For our temperature testing, we measure the peak GPU core temperature under load. A reading under load comes from running Cyberpunk 2077 for 30 minutes.
As for thermals, the reference RX 7900 XT is perfectly fine for dealing with the 315W GPU. The GPU itself peaked at 63C, with the hot spot at 77C. We'll have to wait and see as to what AMD's partners can do with their custom solutions over the next few weeks.