I'd go to
www.crutchfield.com they are pretty good about what fits where. I put 6 1/2" in my doors with the help of Mr. Dremel, but I think 5 1/2" is standard. You may want to consider one of the component systems where the mid-range speaker goes in the door and the tweeter goes in the dash - this gives great detail & seperation. I have one from Infinity and it is awesome. And yes - 5x7 in the back.