well , you answered it non factually
8 million threads on what ceramic coating to use, which stubby antenna is best, etc.
But mention an intake and everyone loses their minds
It's usually the "Which Gen is better?" threads that go downhill fast, but this is going in that direction. The OP asked what the HP gains are on a K&N CAI, options have been made and K&N's Dyno has been provided, hopefully this will now die a slow death.