A V-twin can have a better power to weight ratio than a parallel twin. The engine can be vibration-free without adding counter-rotating crankshaft balancers and associated gears which is desirable if it's to be used as a stressed member for increased frame rigidity. The KTM Super Duke R weighs about 460 lbs wet (440 for the new RR) and puts out over 165 WHP with gobs of TQ everywhere. After riding one, every other twin feels weak. The SDR scaled down to 700 cc, could easily put out 90 WHP stock and comply with the latest emission laws. Of course, you'll pay for what you get.