My 650 is an in-line twin. It has low-end grunt, and a power band from 7k-9k. High torque, but not much horsepower when you rev it out. 600's are in-line 4 cylinders. They're whiny and bitchy sounding, but... The more you twist it, the more horsepower you get. Plus, what I'm expecting to upgrade to, is a super-sport, so the suspension will be an upgrade. My 650 is more like a sport tourer. Looks sporty, but the bars, seat, rearsets, motor, ang drive are all optimized for touring. I will certainly miss that, as a commuter, but nothing fills all role perfectly. If I could stick an in-line four in her frame, I just might. Then, slowly upgrade the suspension bits as I see fit. But I can't. The real downer about switching to an SS though, will be insurance. I paid $83 for the year for her...