The K&N claims up to 11hp. Never seen a dyno chart for one. FSWerks posts their dyno charts for theirs.
The K&N can cause CEL codes. It is fairly common for CEL from such a reputable manufacturer. At least on the FoFo.
Time Attack Stripes
FSWERKS CAI and Race Exhaust
Tint-Windows, 3rd brake light, rear emblems
DDM 6k HID bi-xenon heads and fogs
Short Throw shifter mod