My suggestion for length is legal length(4" down I think), look on your windshield, and there will be a little line on top, where the tint is on your window, and one on bottom, nothing above the bottom line, or below the top line unless you want to be harassed by police all day long. Now about the banners being "rice" thing, I dont really like the solid banners myself. But for the car club in which I belong, our stickers contain lettering that runs accross of the top and bottom of the window Look
here
And I have since taken off the Evolution on the bottom, but does that look that bad? I'm thinking about lower back window maybe? And with DSC's idea about the dark tint and sticker thing, a friend of mine has a black Mopar sticker on the front windshield of his Dart, perfectly in the tint that is like 5% and it looks bad ass, lates