Why not just look at what your state allows? Here's a link to determine what's legal:
Tint Laws
As for tinting the front windshield, unless you have a doctor's letter, it is not legal, at least not quite yet. The tint associations are trying to get some films legalized for front windshields, and have already gotten the legal permission for truckers to allow certain films on their front windshields, due to the amount of truckers who have skin cancer-presumably from driving without better UV protection. I won't go into debating this, but I can tell you that 80% FILM (as opposed to "TINT") on the front windshield of all the vehicles I own makes the interior quite a bit cooler, even in the hot sun of Idaho.
Also, contrary to popular belief, the darker the tint does NOT make it cooler in the vehicle, it actually heats the interior quite a bit faster than lighter tint!
If you want to run darker tint, that's up to you. Its your vehicle, and if that's what you want, then you take the chance of getting a fix-it ticket for it. I run 20% on my front sides and 80% Air80 on my front windshield, and if I get pulled over for the sides (its almost impossible to notice my windshield is tinted, cops wouldn't notice it, as its just that light and done well enough that you cannot see any edges and have no wrinkles/creases), then I get to pull it off and get it checked, then put it back on if I feel like it.
In Hillsboro, OR, the cops there were real sticklers about dark windows, here in Boise, not so much. Same goes for when I lived in SoCal, the town I lived in loved to give out tickets for window tint, but Honolulu, I never had a problem with my old '78 LTD with 5% all the way around!
Point? It really depends where you live and where you travel to. There's no striaght-cut answer here, and it could just be your lucky day to have a cop notice he cannot see who's driving, and feels you need to be pulled over!
So, rather than anyone giving a glimmer of hope that you won't get pulled over for tint, just do what you want and take the consequences if you get busted for it! Don't want to take the chance? Have your local tint shop do a LEGAL film on your vehicle and call it good! You'll never get bugged for legal tint, most cops know EXACTLY what legal tint looks like, and even slightly darker than legal, most will let it go, so long as they can see who's in the car and how many are inside.