No #3 is still good for a 100 amp panel but feed a 100 amp panel through a 60 degree ambient and derating factors can bump it up a lot. I think it would be a hugely bad idea to put a panel in a 60 degree ambient as most of the breakers would trip at values musch lower than the number on the breaker. What would the ampacity be for a 60 degree breaker in a 90 degree ambient? 0 amps