I was going to refer you to "Tuner Performance Magazine", however apparently there site no longer exists. They did do a test with a 00 Si with both sri and cai. It was pretty comprehensive as far as what's out there. If you really want to go off of dyno graphs etc... I would suggest looking to see if someone has the comparison somewhere on the web.
I'm sure there will be some that will come on and say it's a waste of time etc... which is not all entirely true, however not all entirely wrong. Most intakes will reduce back pressure, however most gains are minimal and give maybe a max of 5-7 whp difference. Try this on a new Si and it'll do more and is noticeably more when driving. I say, do what you want, just really depends if you're going for looks, all out performance, low end, top end etc...