XS engineering made a turbo kit for the GTS before everyone else. I can't remember which magazine it was showcased in, but it did produce 284hp @ 7800 RPM.
If I were you I would supercharge. The reason why is because the supercharger works from the belts and pulleys in your car now a turbo works by itself. Which basically means that the supercharger will kick in boost a lot earlier than a turbo. You will get the HP and tourque boost quicker which will be an advantage since our cars don't have much HP and tourque compared to the cars we want to beat ( mustang gt, Z28, Trans am, VIPERS
). Although a turbo would definitley produce more HP because it is not resricted by the engine, the boost does not spool until a much higher RPM than that of a supercharger.