Hi Mark,
I haven't done any direct comparative shots - I felt I had a handle on the comparison just from seeing the files and from memory, but maybe I will: I was thinking of doing the same scene with M240/35Lux FLE vs D800E with Sigma 35mm Art lens vs RX1 vs A7R with 35 Lux FLE and hopefully soon the new 35mm F2.8
My guess is that the RX1 would still win over the 35 Lux and A7R, as well as over the Sigma/Nikon combo: it is a much less tricky lens than the 35 Lux FLE and has sharper edges than the Sigma. However, the RX1, even with colour shading corrections turned on in-camera, is not immune from casts. Of course, the choice of aperture will be key too: at F2 it would be a no-contest, the RX-1 will win hands down. But at F5.6 it might be a closer call between all the candidates, colour casts aside. Overall, if the new 35mm F2.8 can't match the RX-1 lens when shot at F2.8, F4 and F5.6, with colour cast correction and sharpness across the frame at least as good at the pixel level, I will be disappointed. If, when both files are printed to say a 20" print the RX-1 file is a clear winner, I will be a bit dismayed...