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Not too bad for a *handheld* shot, is the digitalbean's image posted above. Jochen, I don't think this image posted above proves anything of the sort.
I would never dismiss the performance of any lens with such subject matter based on such a technique.
Hand holding any size camera and expecting high end definition of distant objects is an exercise in futility. Doesn't matter what the s/speed is, you just cannot hold the camera still enough, especially with 24Mp full frame cameras.
For final resolution of the RX1 'lens at infinity' issue, take a shot focused at infinity, at a good mid aperture (f5.6-f8) with the camera solidly mounted on a good tripod (does not need to be heavy, a good mid-weight CF one will do), and use a cable release. I beleive the RX1 has a nice retro threaded shutter button, if not a longish self timer will do.
Pick a scene with plenty of depth on a clear still day with minimal UV haze. Push the tripod downwards from the base of the head, and wait for 10 seconds before tripping the shutter. My guess is it will be very good, given half a chance.
The image above also has a lot of UV haze, low contrast and washed out colour. None will help the apparent definition in the final image.