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You might also consider the Panasonic LX7. Nice camera, only drawback is the motorized zoom.
I just picked up an X20 a few days ago after checking out a bunch of different options. I'm a D700 user and I was looking for something pocketable with good IQ and handling.
The zoom on the LX7 was the main buzzkill for me as well, though I also found its images to be unacceptably noisy, and its zoom range to be a bit on the short side. I'd probably be happy with a G15, but the viewfinder implementation on the X20 is significantly better, it's IQ is better, and I love its ergonomics and style.
As great as the RX100's sensor is, I just couldn't get around its handling. I don't mind its size, or the fact that it lacks an OVF, but the clickless action on the bezel dial is completely uninspiring. The front wheel on the G15 by contrast can be set to step through discrete focal lengths, or apertures in one stop increments. The fact that the lens is pretty slow on the long end also eats into the IQ advantage of its sensor. On the whole, the RX100 gives the impression that it is supposed to do the thinking for you, with the manual controls added as an afterthought.
The X20 is by no means a perfect camera. I've started a list of pet peeves. I don't need a constant reminder that shutter speeds lower than 1/30 may cause blur; it would be nice if I could turn this and other warnings off. It would be nice if aperture priority would let you shoot all the way up to 1/4000. It would be nice if NR could be turned off altogether for JPEGs, and not just set to -2; the NR does strange things to image detail even at low ISOs. Nevertheless, I think it takes great pictures and handles like a dream. Of all the things it does really well, the one that continues to amaze me is super-macro. The fact that I can focus on an object that the lens is actually touching blows my mind.