honestly, as long as you don't touch the windshield, as far as darkness the visibility isn't impaired atleast not for me because every place i usually go has a lot of lights so looking out of the drivers/passenger sides isn't an issue, it helps a lot to cut down on all those morons with HID's and high beams on.
minneapolis seems similar to jersey in that its all suburbs right? honestly just go with Llumar Charcool 20%. its what i had on my sti, and it was perfect. i know you have a hatch, but it really wont be much different, i say do 20% all around, and do LLumar Air blue on the windshield so that the forward visibility isn't affected.
on the brz i have a hard time judging distance backing up so i ended up installing a back up camera, but one thing that will get hard is backing up in poorly lit areas, especailly when it is raining. had a tough time with my sti but it was infinitely better when i got brighter reverse lights. its sometimes hard to focus so i'd recommend a back up camera if you dont have one already.
also there really isn't many increments in % most places go from 20% right to 35%. unless you can figure out some kind of way to get those dots out of the windshield, dont do a strip....or get and STi windshiled. it has a tiny strip built into the glass. you can see it in some of my photos.
that strip was factory, i dont understand why subaru doesn't put that on the wrx as well, i think that would solve your problem, i had my radar mounted behind that strip, couldn't see it from outside at all and it was perfect in blocking the sun form my eyes. i personally dont like tint stripe because they just look out of place, because they dont fade, this OEM strip fades and is sublet know what i mean?