Heat as well as altitude can affect the lift. Hence the reason when they built the new DEN airport they took all that into consideration and then some. With their 16000 foot runway Id imagine they can take off if its 120. You would also find that most airports in the mideast, Africa, and other places where it gets well above 100 quite often also have 14 or 15000 foot runways. Not sure why they didnt plan for that at places like PHX