You never gain HP by using CF. You can reduce weight thereby improving the weight to HP ratio improving cars performance. However, the minuscule amount of weight added to parts will have little or no impact on performance (uless you're looking for 100's of a second improvements).
The CF does make the stock OE parts stronger and more resiliant and look better. No different than the guys that buy CF hoods for daily drivers. Those are cosmetic mods only beause they weren't purchased (for the most part) for track cars, but to "dress-up" their street cars!