Great writeup, Ray. Very insightful points, and great photos as always!
I think this point needs some qualification:
In general, when comparing two formats with similar sensor technology and similar base ISO values*, the larger one will have an image quality advantage under two circumstances: 1) when light is plentiful such that both can be used at base ISO; and/or 2) when a more shallow DOF than the smaller format can deliver is
acceptable. Note that I say "acceptable", not "desirable".
Say for example you are shooting the X100S at f/5.6 because you
need as much field as that camera gives you at f/5.6 and that you're forced to shoot at ISO 1600 because you
need the shutter speed that ISO 1600 gives you. Sure you can shoot the RX1 at f/5.6 ISO 1600 and marvel at how much nicer and more malleable the files look, but if you really
needed that DOF, then your RX1 has to be set to f/9, and if you
needed that shutter speed, your RX1 will now use ISO 4000.** Now is that ISO 4000 RX1 file still more lovely and malleable than the ISO 1600 X100S file? That depends on the specific sensor technologies of those sensors, and it may well be, but it's no longer going to very noticeable to most photo enthusiasts.
My point is that we tend to always think of the ability to go more shallow as a bonus but under any shutter speed limited, light constrained circumstances where you are
unwilling to go to more with a more shallow DOF than the smaller format can deliver, there is no image quality advantage inherent in the use of a larger format.
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One comparison you didn't mention unless I missed it is size - Are these cameras similarly coat pocketable? If so, does that still apply with the EVF on the
Sony? X100S strikes me as a bit easier to grab and go, but I haven't spent a lot of time with either, and I'm pretty size sensitive (eg, my E-PM2 feels more coat pocketable with the P14/2.5 than it does with an O17/1.8).