There are so many tens of thousands of cars here in Southern CA that have dark tint on every window (including the windshield) that it's a complete joke. You get the tint ticket when you get pulled over for something else, like speeding in your P90D, not just for driving with tinted windows. I've had tint on all my cars for the past eight years and never received a ticket for it. Granted, once in a while some poor sap might draw the short straw and get a cop in a bad mood who hasn't met his/her quota, but otherwise you can tint here and not worry about it. Don't know about other states, though.
I highly recommend Hüper Optik ceramic film for your tint since it has the best visibility for the driver and has excellent heat reduction. It also doesn't interfere with electronics or antennae. I generally use 40% on all windows except my windshield. Considering how large the Model X windshield is, I may consider putting a 70% film on it if I discover the CA sun wins that contest.