When I got my windows tinted, I just wanted the front two windows to match the back factory tinted windows. Like someone else said, Ford's tint is 18% (squirrly number...go figure) so I just had the guy put 20 on the front windows. Didn't want it dark enough that I couldn't see out at night, but darker than 35 or whatever. From the inside, you can tell a slight difference between the factory and aftermarket, but from the outside it is nearly identical. I also had another guy put a dark strip along the top of the windshield (don't know the light transmission number).

Just my 2 cents

 

That is what I was thinking about doing... got any pics?