Depending on where you're going, I made the same trip back in July (to pick up my new car).
We were speeding the whole time and total we saw 6 cops. Had a radar detector which probably saved me a few times.
Interstate is definitely the way to go though. We took 69/169 most of the way down but interstate back. The way down was great scenery, Eufuala Reservoir was really cool!
But in a hurry, take 35.
Don't "think outside the box".
There is no box.