I have the 1Ds MkII and have no problems using it at any ISO setting - especially with some NR applied.
Here is a 100% crop of a shot taken at 3200 ISO (not RAW - I almost always shoot in JPEG large nowadays):
It was taken on my 1ds MkII with 0 sharpness applied and all NR turned off to preserve as much detail as possible.
The noise is fairly fine grained even in the shadows and even a large print would be acceptable at normal viewing distances.
Here is the same shot after going through Neat Image (set to retain finer detail)
There is still a small amount of noise but very fine.
and here is the final print after going a second time through Neat Image and PP and reducing in size:
I bought the 1Ds MkII over the 5dII because on the 5dII it seemed to me the lower noise at higher ISOs was achieved at the cost of some detail even with all NR turned off of the 5DII.
Also an important point about higher ISO on higher pixel cameras is that as the pictures are reduced in size so will the apparent noise.
So the old instructions we used to get in the days of film about filling the frame as much as possible with the subject is equally applicable here because the less cropping you do the less apparent noise in your final print.
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