Most TT exhaust will give you the same gains as long as they are dual with at least 2.5" piping. 3" is not needed. Sound, quality, and looks are the big differences. A select few are angled like the HKS hiper, and a few have 4 tips. Those are all the more rare ones I prefer a nice stainless system with oval cans. Z Fever sell one like that which sounds very good. The stillen ones are nice, but i dont think look as good. The greddy isnt bad and is pretty reasonable for a full stainless, but in my opinion sounds the worst. To me the greddy Evo sound worse than the greddy SP. The HKS hiper sounds and performs well, but is angled heavily which is a matter of taste. It is also not stainless and significantly cheaper. Mostly because of its price, it is almost always on back order. Hope this helps