i've been working on a Tamiya Jaguar XJR-9LM lemans car for a while now, and have been using the spray through a nylon method on a lot of the underpanels, and it works quite well.
I shoot first with semi-flat black, then shoot gunmetal metallizer through a nylon that has been very carefully placed and formed so i get the pattern i like.
I like going the nylon route on the undersides, because the 'mesh' on a the underside of carbon fiber (at least the carbon fiber on the car i'm doing) is very small (a grid of like 1/4" squares), the decals by scale motorsport, the grids are scale to like 1" squares, which is way too big..
plus, the color difference is very subtle... just enough to look real, but not too much to look phoney.