Man....I'm on the fence with regards to the high-ISO images taken with the D4 in comparison to the D3s. It's very hard to compare them currently, as I don't have both cameras in possession - YET (should have one of the first batch D4s in 2 weeks). I'm very impressed with the D4's sample images, even @ 25k and 52k ISO, but my question remains, does it oust the D3s @ high-ISOs?
Here is my prediction, based on my in-depth studying of the D4 images as well as my own D3s images.
1. I agree that the D4 has a 1-1.5 stop advantage in DR, over the D3s, especially @ base-ISO
2. I think the D4 has better saturation @ high-ISOs than the D3s
3. I think the D4 will just barely beat the D3s in SnR, but will handily beat it in DR and Saturation, so the IQ will appear more pleasing in the D4 images. The extra detail from the bump in resolution will also help retain more detail after DeNoising, which will also help the D4's images to look more pleasing, when compared to the D3s - all else equal.
4. The D4's video output will be much more appealing @ high-ISOs as well. I think this is where the D4 will really shine, over the D3s' very limited video (720/24p).
in summary: The D4 will be the new king, even if it's by-way of the perception of a better image. As long as the D4 sits squarely with the D3s in the SnR dept, the advancements in DR, saturation and resolution will give the D4 the absolute advantage at native resolution, but especially if you down-sample the image to 12.1mp and compare with the D3s. If the D4 slightly back-slides in the SnR dept, the image quality might be about even between the two, just with more resolution - which would also be welcome, yet slightly disappointing. This would still likely give the D4 a perceived advantage when down-sampling to 12.1mp and at least a sharper image from the added detail. I think the latter is less likely, though; this is Nikon we're talking about.
As long as Nikon is on schedule, I should get a copy of the D4 in about 2 weeks. I will immediately post some comparison images of the D4 vs. D3s, on the main blog. They will include some low-ISO comparisons, but mostly high-ISO comparisons because this area of IQ is the most talked about and the most unknown. I will go more in-depth in the full review article that will be published a few weeks after. It's going to be interesting, indeed!