I can offer a little advice, having a Panasonic G3 m4/3 camera and a few lenses for that...and I just picked up the Sony RX100 two weeks ago. I would say overall image quality, they are very similar and that includes noise at higher ISO's. Obviously, the G3 has the advantage in flexibility when it comes to lens selection...But I've been impressed by the RX100 as well. Yes, it's a little slow on the long end. But you can still get some decent depth of field, throughout the range.
I think you need to think of your choice differently...it isn't so much about specs but your intended use...If you own no other camera, then go with the OMD. You have more lenses to choose from and more flexibility. To me, the RX100 is the step up for a low-end point and shooter OR...it's an excellent second camera for a more serious photographer who already owns a higher end DSLR.
If I'm heading out for the day and my goal is it strictly shoot photos, my Canon 5D Mk3 and a few lenses come along for the ride. The G3 used to be my "I want a good quality camera, just in case camera"...meaning, I wanted a good camera with me, but my focus that day might not be in taking photos. Now, the RX100 has filled that role...especially given it's size, I can literally put it in my pocket and go. No camera bags, no lenses...just a good tool I can have on me to take good photos.
This is EXACTLY how I would approach this decision since I too have, from what it sounds like, the same equipment and methods of operation as posted above. Since buying the RX-100 I will be selling off all my M43 lenses and G3 bodies. They do have excellent IQ but the M43 bag has gotten to be now the size of my DSLR bag and lenses. It now defeats the original purpose of downsizing. The RX is a great point and shoot camera and that is all I intended it to be.