Yes you should drain the oil out. The real reason why is, when you have too much oil in your motor, it pools up around the crankshaft, as the crankshaft turns, it looses momentum, which will hurt performance. Yet that's still nothing to the fact that, as the crank turns and slaps the oil now at it's level. The oil will begin to foam up, as more and more oil foams, your oil pick up tube, will suck up this foam vs actual liquid oil. when it does this you will have foam running through your whole motor where oil is supposed to be. What does this matter? Well oil is needed not only to keep metal parts from touching each other completely, but it also helps cool the motor. Foam in a motor will result in the motor blowing due to either overheating, or the metal parts rubbing directly against other metal parts. (ie: rod bearings rubbing directly against the crank) which will cause them to wear and break.