I had my Merc done with 20 all around, and had them use a ceramic coated tint for maximum heat blockage. Mine goes all the way to the top of the glass on all for windows. I also had my windshield done with 40 or 50, something in that range. I was afraid about it at night, but it's just like normal at night. I don't even notice it. But it blocks SO much more heat. Of course, the entire job is illegal as hell, but they don't bother me in the Merc. I live in Charlotte, NC, and they would ticket me if I was in a riced out honda, but they really don't bother cars like mine, unless they have a reason to, then they will use that as an excuse for more tickets. They sure love to get speeders here, no matter what you are driving.
When I had my tint done, it was a Sunday and the shop was normally closed. The owner was in doing only two jobs. One was mine, and another was a CMPD cruiser. The officer was having the tint on his new cruiser done at his own expense, and it was 20 all the way around, with 35 on the windshield. He was in the shop, and at first I was a bit worried, but he told me that it doesn't matter. He said that he wouldn't pull anyone over for that unless he had a another reason.
The only trick here is getting a guy that will give you the inspection sticker. Most of us don't have a problem with that though as everybody and their cousin has an inspection license now.