i beleive that the upgrade in diameter (from the corksport or aftermarket) inlet pipe has not to do with hp, but with smoother/ more audible turbo feedback.
as for anyone wondering about intake hp increased, its noticible/visible on a dyno at top end only (most intakes for the DISI2.3Turbo in general grant avg whp increases of 10+, it obviously enhances turbo noise, throttle response, intake noise, and increases the redline by 100rpm each bolt on gradually increases this until its fixed from a tune or new turbo. also i've heard a +1 in MPG from everyone who has one.
I think i will get the cobb, the corksport comes to 300 with shipping and tax, and im all about the 185 free shipping and 99$ group buy inlet (larger/black) i seen on here.