I'm a fan of the AEM Brute Force. They should be CARB exempt or at least certain models are according to their website. The performance gains are about the same, maybe a little more, than the K&N. Figure about 8-12 hp -- no tuner needed.
My draw to the AEM was their "Dryflow Air Filters" and polished intake tube. The Dryflow never needs oil which usually = less down time between cleanings and zero chance of over-oiling.