Motorcycle Questions?

So I've been thinking about buying a motorcycle and heard the Ninja 250r is a great starter bike because the engine isn't too powerful, and easy to learn on. What's the maximum speed on one? Without burning it out kind of thing? Because I see 125cc bikes as well for sale, some cheaper than the Ninja. And what's the maximum speed on a 125cc bike? The 125cc bike is a 2008 Honda CBR.