yea, the real stuff is super strong.
IIRC the grey is stronger than the black. they both use acrylic adhesives but the black is foam based.

I have an s13 coupe. Its not a silvia, as we got the ka24de and crappy pop ups. But I'm in the process of building a mosnter SR for it, 650rwhp on pump gas. PLus caging it, etc.. RHD conversion, silvia front end and what not