The compression on the 650 is pretty low so there should be no need to run anything higher than regular and the owners manual would tend to agree.
A very common misconception is that high octane fuel is more powerful, it is not. It is actually harder to detonate, thus allowing higher cylinder temps before pre-ignition becomes a problem. If your vehicle can run full timing advance at a given octane rating with no detonation, increasing the octane further will actually cost you power and economy. That's the theory anyway, I have recently decided to put it to the test. I keep very close records of my fuel economy and have tons of data on the kind of mileage I get with regular. I figured I'd run premium for a while and see what happens. I fully well expect to only gain a lighter wallet, but this sort of thing interests me so I'd like to back up theory with my own data.
As some others have mentioned, ethanol blended fuels can be a big problem. Most vehicles will run just fine on e10 but the stuff degrades VERY quickly and can cause serious damage to your fuel system if allowed to phase separate. Thus you need to examine your riding habits. During the summer I ride my bike as much as possible and burn mostly e10 gas. The reason being that there is only one station in my town that sells pure gas and it is usually $0.30 per gallon or more higher than e10. Over the summer it is rare that gas will be in my tank for more than a week, so I don't worry about it too much.
Now fall and winter is a different story. Weather patterns are so stupid here that it can easily go from perfectly comfortable to ride to parking the bike for the winter in just a matter of days. As such when the weather starts to get colder and I might have to park the bike for an extended period at any moment, I start to fill up with ethanol free fuel and I go the extra step of treating that with Amsoil fuel stabilizer. I make it a point to do this for several tanks before I have to park it just to get the most ethanol out of the tank as possible. Consider this, it's a 4.2 gallon tank. If it has 10% ethanol and your fill-up is only 3.2 gallons of 100% pure gasoline, you still have 2.3% ethanol in your tank. Do it again and you are finally under 1%. Is this overkill? Probably, but if you've ever dealt with ethanol related fuel problems, you'll understand why I do it.