that is definitely an aftermarket exhaust. The stock exhaust is very quiet. You are probably running 5 to 8HP higher than a stock bike, if the jets were set right with the other mods.
You probably have not hit the peak HP on the curve yet - its about 55mph in 4th gear, and 70mph in 5th. If you get on an interstate and shift into 4th at about 30mph, and crank it WFO you will feel it take off and start growling at 55. Shift into 5th at 60mph and it will do it again at about 70mph.
Or if you really want to feel the power curve - shift into 5th gear at about 40mph and then hold the throttle wide open. It is an incredible thing to feel the bike accelerating faster and faster as your speed is increasing.