My opinion, is that on its own an intake doesn't do much other than look cool and sound good.
With the ways cars are controlled by computers these days you could put a huge cone on the front of your car leading into the intake and see almost nothing. The computer is going to adjust everything to compensate to get the car to run the way it is supposed to. In order of what I did to my car was 1)Intake 2)Full Exhaust) 3)Tune.
With the intake the sound change was the biggest factor no noticeable performance gain. The exhaust bumped me a good bit on the butt dyno but as it should. I got a full magnaflow system to include cats. Now, even with those things the computer was still in charge. Once I got a Torrie tune, holy ****. Much improvement in almost every department but I'll stay on topic here with the engine. With the ability to intake more air and get the exhaust out quicker the tunes Torrie made for me, MPG...Performance....and Performance + 2 degree's of timing, made a world of difference. I haven't tried MPG yet, maybe on a long trip or something. I also haven't tried performance +2, just performance. The car is noticeably quicker. It's not like adding a turbo or anything I mean you have to be realistic. I'd estimate 10-15 in gains on both HP and TQ. The shift speed increase is really what gets you going quicker.
I use the Torque Pro android app and a OBDII bluetooth adapter. It's not exact but it's close enough. I've launched to 60 in 6 flat before according to that thing. It was 6.6 with just the intake.
Again, the ability for the intake to make some gains is there. It doesn't take a rocket scientist to see the obvious improvement in flow path and resistance, but you have got to modify that computer to actually use it.