I just installed the SU boost tubes three days ago. I only did this because I stripped one of my clamps trying to tighten it down, and figured I'd go ahead and do the boost tubes for the heck of it. I think there isn't much noticable gain at all from the tubes themselves. Unless you've replaced your turbo or something, the stock tubes will be just as effective. What you should definitely do though, is make sure all four of your boost tube clamps are tight. They come pretty loose from the factory and tend to loosen up as time goes on. Just make sure you don't strip one of them like I did!
