I haven't ridden the Ninja 400, but I really like my CBR500R. The bikes are supposed to pretty similar in terms of horsepower, but the CBR has more torque. I will say that my CBR is already a little bit spun up at 75 MPH, so I'm not sure if I'd want to have even higher RPM at that speed. Also, the CBR is really well engineered. My fairing provides pleasant wind control and the mirrors do a nice job of blocking wind from my hands.