if they are fairly new and not worn in, i'd do one, if they are old i'd do both.
but its got to be the same brand, front and back, if notand you go for a different brand, then its all 4 to change.
i like the stillen rear quater covers as well, but i fear i may be run into the ground if i bought and fitted them.
i could see them in CF to match the b pilllars
i bet it would cost more than a turbo conversion.
if you were pushing the boat out, you'd transplant the engine in as well if your doing it you might as well go the whole hog