Re: infinity or polk?
I would go with a 6.5 inch set up if your building your kicks. you'll notice a little better bass responce out of them. i had 5.25's and upgraded to rainbow 6.5" in my dash the sound quality and wider Hz range of the 6.5 dominates the 5.25.
but thats just my two cents
By the way the new memphis PR class Comp's are $150 retail and sound good for an inexpensive comp. set
Audiobahn is like the Jessica Simpson of the car audio world, sure they might be pretty but its nothing you want to listen to...