Looks like the the Clubsport side skirts will fit directly to a MK7 GTI or GTD. The assembly overview and removal and install instructions are identical between the two on erWin so it appears as you mentioned that the only difference is that one is painted gloss black and one is not. It is the Golf R and Golf R Line which have different side skirts that mount in a different way. Still, you'd get your original side skirts painted two or three times for the same money as a set of C.S. side skirts so that would be the best option.