I've been very happy with my MarcyMotorsport intake. I have over 20,000 miles on the car with the intake without a single problem from it. The gains for it are solid and posted, all you ahve to do is go to his website and you can see the before and after dyno's of my car with the intake.
We've had both the FS and the Cosworth. Either one is great -- the Cosworth is combined with L1&2 on our wagon, so it's hard to compare it 'stock-wise' to the FS. The Cosworth piece by itself is extremely light and well-made.
We had the FS intake with a cat back Magnaflow on our sedan, and the FS intake with Borla cat back on the wagon -- definitely more hp on the butt-dyno on both cars.
On this car, you are pretty much going to see the same gains with an intake, roughly. I have learned that the MM and FS are about equal, just like hidrive said. You just have to decide if you're willing to pay more for the polished finish.