I am running it on the 4.7L. Also CAI / catback. From my perspective what it did for the 4.7 is give it a bit more pep from stand still - also seems to have better torque through the curve - nothing earthshattering, but the tail off seems to be not as steep up in the high rpms. Mileage is highly dependant on your drive style, so hard to comment there.
As for HP gains - well, you might eek a few more out. I know the CAI folks claim, 10 hp, cat back 15 hp, chip "up to" 30 hp. All in all I am certain I am not pulling 55 more HP out of the engine, but it does perform nicely. If I had to guess I would say maybe from 238 to 250 with all three mods at peak HP. Not bad, but that is just a guess. Do I think its worth it? Yes - if you already have the other mods done.
Not sure if that helps.