What is the base ISO of the Sigma DP2M?

It's a question that I asked myself when the DP's First arrived. What is the lowest ISO that the Sigma DP2Merrill was designed to work at?  - What ISO that produces the cleanest most natural files?  

I conducted my own tests and concluded that this was ISO100.  Recently though, having read around the subject:  at least one notable commentator (Laurence Matson Via Sean Reid) , himself quoting a source 'close to Foveon' has said that the base ISO of the Sigma DP2 Merrill is ISO200 and that ISO 100 is effectively a pulled exposure setting.  I was excited and delighted: more speed without sacrificing image quality - excellent news.

I did find this news puzzling though.  I'd done lots of very dull testing at various ISO's to figure out the performance of the camera in different situations and I constantly found more noise in the 200 than the 100.... Not unusable but not as clean as the lower figure, so the information apparently from Sigma itself was certainly worth investigating. Here are a couple of shots that demonstrate again what I've found, and what leads me to believe that ISO 100 is the base ISO and not a 'pulled' exposure.  I hope I'm wrong and would welcome input from knowledgeable friends?

Bokeh detail from a test image taken at ISO 100 with the Sigma DP2. Viewed at 100% in Simga Photopro (Click to view)

Bokeh Detail froma test image shot with the DP2 at ISO 200. Viewed at 100% in Simga Photopro (Click to view)

To my eye the shot at ISO200 shows micro banding and more noise than the shot at ISO100.  I've tried to do a straight conversion in Sigma Photopro and left the setting at that coming from the X3F file.  Then zoomed to 100% and taken a screen  shot.  

Now I'm not saying that this is a problem per se.  I think both are perfectly fine files and ISO200 is certainly a fair setting if light levels require a bit more speed - but my question is.... what is the base ISO of the Sigma DP2 Merrill?  Evidence seems to suggest that it is 100, but respected commentators contradict this!

If anyone knows better, then please email me as ever your input is really welcome?  I'm going to do more research - I'll update this item once I have more information. I plan to test the DP1M as well as do more tests of the DP2M.   

This thread on DP Review includes a post from Laurence where he makes his assertion.