35% Onyx film on the windows, 55% on the sunroof. Heat wise, I've got a black car...I know about heat. The difference in temps while the car sits in a sunny parking lot at work are extremely noticable.
Keep in mind what was said by many, the QUALITY of a film outweights the darkness and the UV protection has nothing to do with the darkness.
I have always been against tint because it'* negative effect on night/bad weather vision. My experience with the Onyx film is contrary to that... vision is the same as before, the tint has not effected it at all.
Qualty is the key.