So an O-ring chain is slightly heavier, and has slightly more drag.
Compared to the frictional losses of motor, clutch, gearbox, chain-onto-sprocket-teeth, wheel bearings, brake drag, etc, and the weight of all the rotational and non-rotational parts... Let's just say that if anyone says they can feel the difference between a plain chain and an O-rig one, I will call them a liar to their face.