Yours came with an O-ring chain? My MXR had a Regina non-O-ring, the master links sucked (replaced w/D.I.D. 520NZ links, perfect fit) but the chain itself held up OK for 2.5+ years/3K miles.
My bikes came with non-O-ring chains. They were both noisy as hell, and they both stretched like crazy from Day 1. I would have to tighten the chain every ride or two.
Frankly, I didn't really notice any additional drag with the x-ring chain, although the chain was fairly stiff going on. There might be more drag, but frankly, I just didn't feel it. Of course, I'm a slowpoke map 1-2 rider, and I use regen all the time, rather than brakes. So maybe I'm just used to the regen, and compensate with the throttle. My battery life definitely hasn't gone down. But I'm definitely enjoying the new sound. Sounds much more smooth, rather than jangly like the stock chain.
But my brake pads sure last a hell of a long time! I don't even think I've gone through 50% wear on either bike yet. Silver linings, right?