All strains like a different temperature and humidity. Tropical strains most likely enjoy high temps and high humidity, while maybe a Northern California strain likes it cooler with a heavy temp drop at night. You really need to experiment and play around.

However, I would never let your grow room go above 80 degrees F. Beyond this temp, you really need to be supplementing CO2 because otherwise the stomata will open to much and there wont be enough CO2 to take advantage of and you might experience the negative effects of to much heat. Now if your temps are at 90, and everything looks perfect, I wouldn't change anything. If they are at 90 and stuff is slow, etc, then I would change it.

There is also a difference between 90 degrees in a box with low circulating and fresh air exchange and 90 degrees in a box where there is lots of air movement and lots of new fresh air coming in. The latter will always be better.

One more thing to remember is that if your thermometer reads say 80 F and its placed somewhere in your box or room, unless it is right under the hood where the canopy is...yoour not going to get an accurate idea of what the real canopy temps are...and thats whats most important. When it is 85F in my big hydro room, right under the canopy where the buds are is 90F or even higher. Thats why I try to keep my room about 5 degrees lower then what I think the canopy can handle. .