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I couldn't find it, has anyone ever compared 35mm R Summicron V2 with Sony RX1?
Since no one else has responded, I'll take a swing at it. My opinion comes firmly from the peanut gallery, as I haven't done a direct comparison, but I've looked at both lenses/systems so maybe my ideas could be useful for you.
From what I've seen, the RX1 lens is very, very good. It is a superior optic to the Summicron. If anything, the Summicron is better corrected for colors--the RX1 has a slight bit more longitudinal chromatic aberration than the Summicron--but the RX1 edges out just about everywhere else. Resolution across the frame, focal plane flatness, distortion, and flare favor the RX1 from barely to significantly. Flare is a major difference. The focal plane shape of the Summicron, which I believe comes closer in the midzone then toward the distance toward the corners, can either be a blessing or a curse; most photographers prefer a flat, predictable focal plane.
The reason I like the Summicron but have no interest in the RX1, though, even though I shoot Sony cameras, is that the RX1 lens is permanently attached to a camera. I'm expect that, eventually, others will succeed in re-mounting it to, say, the then-current A7R, but then it will become permanently attached to that camera. The Summicron design is 40 years old and will still perform just as well 40 years from now. The only thing that will obsolete the Summicron is if curved sensors become so predominant that flat sensors become prohibitively expensive to obtain, which I strongly doubt will occur in my photographic lifetime. On the other hand, the RX1 might not function well in 10 years, not to mention 40. The electronics might fail. Batteries might not be available. When a ten-cent circuit failure might ruin my ability to use one great optic, but a slightly less stellar lens is available that will take substantial abuse and keep on delivering great images, I'll take the more reliable lens without hesitation or doubt.
Well. With one qualification. If I saw a scene that I wanted the highest possible quality capture of, and I had the choice between an RX1 or a Summicron 35, I'd probably choose the RX1. (If it were a bokeh-heavy scene with high contrast subjects, I'd choose the Summicron, but that's because I have a pet peeve for longitudinal chromatic aberration and not for any rational reason.) For today, the RX1 is the superior lens. For the purpose of having a reliable lens in my bag, though, not to mention spending my money on the lens and hoping to use it well into the future, the Summicron would be my clear choice for today as well as tomorrow.
Hope this helps,