It (the stock box) may look more restrictive but it isn't. When I had my AEM CAI I put it beside the stock piping and checked it's lenght, the degrees of the elbows and it actually turns out that the CAI had more bends (it has an extra 45 degrees) than the OEM box! And it'a also longer.
Since I've lost the Calloway elbow ages ago, I've put a longer flexible aluminium tubing that goes right to the headlamp, there's a lot of high pressure cool air coming from there. I also use a flexible heat-shield (a Termo-Tech shield for a cat converters) on the left side of the box and over the tubing to cut the hot air coming from the fans. It's very simple.
I did quite a bit of testing (also with SRI and such), and I use a short "test-strip" (in an industrial area, when nobody's around) and regardless of butt-dyno feeling, with the stock box I get a higher speed (130 Km/h, 3rd gear, compared with 125 Km/h with other setups) before my braking point (there's a fire hydrant that I use as a mark). I've done many passes and it's consistent. Maybe at high RPM the CAI is better, but it seems to lose some torque at the bottom. That's my guess. First and second gear have more torque with the stock box, I'm quite positive on that