Well as far as top speed goes, theyre not rated much past 120 or so in stock form. I'm in FL, which is pretty near sea level, and I got mine up to 125 mph indicated, bone stock. I haven't tried it with the exhaust, but I doubt it will do much over 135...mainly because of gearing. At 125, I had about 1000 rpms left. At 135 I imagine you'd be right about to bounce the limiter, which as far as I can feel, comes in at about 11,500.