A little comparison:
Lots of people claiming that the Sigma Quattro generation improved ISO performance over the Merrill. And whenever a new firmware or SPP version is out, i'm doing my tests.
Sorry to say, but it's a myth. In my opinion Quattro is not better. It is worse, or maybe "equal in a different way". Quattro improved slightly over the last month due to better NR in SPP, but
it is still far from "better" than Merrill.
So here we go: SD1 vs. DP0Q
ISO 1600, same shutter speed, same place and time. SPP luminance NR OFF.
Quattro has less color blotching than Merrill, but it also desaturates the colors more, so there is obviously a different/stronger color noise reduction going on.
I see more and uglier luminance noise in the Quattro images. I would always prefer the Merrill over the Quattro for black and white images at higher ISO.