if you want a great bike that has a lower to mid powerband is the suzuki sv650. It doesnt have the best top end, but in the twisties its one of the best because the low end power is geared right. Its also 650cc bike, so its in the range you wanted. Now what we need to know is what experience do you have with bikes, if you have experience, then you can go for whatever bike you want because you driven bikes before, but if none to just alittle bit, then a ss bike (cbr, zx-6r or bigger, r6, r1, and gsxr) would definitely be way to much power. Its something that you have to be truthful on because a bike with to much power can hurt you or worse. The sv650 though is good for a beginner but has the power your talking about..