35% is hardly noticeable, since I have it on my windshield. I would go with either 15 or 20% all around. You won't notice it is dark from inside the vehicle, but you will enjoy the feeling of not been seen outside and thinking you are in aquarium.

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2010 BMW X6M (future car)
2006 BMW M6 Indy red/Portland Brown (sold)
2004 BMW X5 4.8is Silver/Black
2002 BMW X5 4.6is Black/Black (sold)
2004 Lexus RX330 Gold/Ivory (sold)
2000 Lexus GS 400 (sold)