Hi Stose, I own an 09' 950t, and I upgraded my exhaust, air kit, and added a fuel processor since these bikes are fuel injected. I'd heard several systems on the 950's. The 2 into 2 looks cool, yet for me they were way too loud without installing aftermarket baffles. I went with the cobra 4" slip-on, and love the sound. I saw a marginal difference in performance, and no noticeable difference in mileage. I wanted more, so I bought cobras fuel processor, the f2000i, and the LA choppers XXX open air kit. After I installed both of those, different bike, even with the stock emissions in place. After my Memphis shades batwing install, it performed better as the wind was going around me, and not hitting me directly like with the stock tall windshield, but those were my experiences, some one else may have different ones. When these bikes are built, they are very lean to pass epa regulations. When you let those engines open up and breathe, they can keep up with larger bikes with minimal loss if any in mileage. This spring I'll be having my bike dyno'd and dialed in locally. I'll post the results once I've completed it.