If you are a math freak or a pixel peeper, the 1DsMkII probably isn't for you if you're all uptight about ISO noise.
The reality is, this is close to a 5 year old model at this point. It's high ISO performance is probably the last reason on earth to buy one verses another camera. a 5DII will smoke it in that the department. That said, there's far more to life then high ISO performance and the 1DsMkII has numerous benefit features that have been repeated over and over and over again.
Also, as I see you asking for comparisons of noise in 1.3 and 1.6 crop bodies, I have to wonder just how preliminary your search is for a camera body, if you haven't at least made a firm decision about wanting/needing a full frame sensor body? Do you shoot a lot of wide landscape and portraits? Theses are the traditional users of full frame bodies because they need the full potential of the lenses for width and depth of field.
If you're not sure about these things, there are numerous threads here to help you through that thought process.
Indeed I am in the midst of doing my research on the 5D2 vs 1Ds2 decision. I understand that noise control isn't the best thing to go for in the 1Ds2. I currently have a 400D and have a 1DIIn reserved from a member here. Those 2 cameras have imo very similar ISO1600 noise amounts, and I regularly push my 400D to iso3200 in post, with NR and it's fine.
However there are reviews out there that state that the 1Ds2 has the same high-iso control as that of the 1D2 (and thus, similar to my 400D), whereas from 100% shots I've seen, the 1Ds2 is on par with a 5D, which is better than the 400D. Difficult to correctly determine I guess.
I know I want a full frame camera because I borrowed a 5D2 and shot well with it last time. I also borrowed a 1D2 to shoot sports and loved the AF and built and everything 1 series. Short of getting canon to churn out something like a Nikon D3, I feel that the best compromise between IQ, Speed and Price is the 1Ds2.