This is definitely not a scientific test, but rather something that correlates more closely to my working methods. In many cases it's just not practical for me to shoot ISO 50. We often have people in our shots, are using strobe where multi-popping is counterproductive and occasionally shooting through a polarizer.
The Sony and Canon were shot at f/11 2 Sec Iso 100. The IQ 260 was shot at f/8 2/3. My initial exposure of 2 Sec just felt too bright on the IQ 260, so I used my 1 Sec exposure for the test. When I process the 2Sec exposure to match the tonality of the group it DOES have better shadow noise, but the hilights don't clip as nicely. I usually shoot to protect the hilights as much as possible (probably because I shot transparencies for 15 years).
Of course each of these images would only be at the very beginning of my postproduction flow and different techniques would be used to help each along. All would have darker windows blended in. I might revisit the brighter IQ260 file to use as a base and just as you can use darker exposures to recover hi lights, I sometimes use brighter exposures to clean up shadow noise (by processing them @ -X to match the base exposure and masking for just the shadows).
Perhaps the best test, for me, would be to proceed and retouch each to be the best possible image.
For now this tests has shown me exactly what I wanted to know... The A7r can and will replace my 5d2. While it won't replace my MFDB system altogether, it will take over some of that shooting.
Coming from years locked into shooting 4x5 Transparency film as the only possible workflow, I gotta tell ya, I'm damn giddy to have so many excellent tools at my disposal.
ps I've added the brighter IQ260 RAW file to the DropBox if anyone wants to play with that.