I've had an ITG on mine for over a year now. I can't say I've noticed much performance difference over oem, very slightly quicker through the revs perhaps. I was disappointed that I can't hear it, but that being said, the only bit of sound proofing left on my car is the bit under the bonnet and my exhaust is as subtle as a half-brick to the face, so not surprising really. Very nice piece of kit though, well made and lovely to look at.
There's a quick cold air feed how-to on post 238 of my build thread (that's page 12 for me on 20 posts per page). Yes, it's a bumper off job, headlight and battery too ideally.