Ive seen a few shots from the D3, and although they are the best Ive seen from a Nikon(noise wise) The Canons still have the edge. Until I see more I am not willing to believe any of the claims.
You havent said what your primary use for the camera would be, but based one the limited info Nikon is providing, and the few reports coming from a small amount of people that have gotten to use the the new nikons I will make a few comparisons(I reserve the right to change my opinions when more info is available). IVe owned a 5D, and currently own a 1D M III and 40D.
1. The first thing that jumps out at me that Nikon has yet to confirm or deny. Both cameras lose FPS when shooting in RAW mode. The D300 goes from 6.5 FPS in Jpeg to just under 3 FPS in RAW mode, and the D3 goes from 9 FPS Full Resolution Jpeg a second to 4.5 FPS in RAW. The 11 FPS is only available if you shoot with DX lenses wich limits the camera to 5 Mega Pixels.
2. The D3 isnt a true FF sensor, it is actually a 1.1x it is very close and may not make very much of a differance, but still isnt technically a FF camera.
3. The 5D is less than half the price of the D3, has the same Mega Pixel count(actually a bit larger but both are 12 MP). The 5D is a tre FF camera, and based on some of the Example I have seen the 5D still holds the High ISO title.
4. The 1Ds Mk III still is unchallanged by anything for total resolution( in the 35mm DSLR arena). So if you need the most resolution pssible from a 35mm style DSLR the is no other option.
5. 1D Mk III. I have had no issues with focus on mine, and Im sure the issues other are haveing will be fixed before the new Nikons hit the streets. the 1D3 is capable of 10 FPS full res shots regardles of Raw or Jpeg. There are some Nikon Sports/Wildlife shooters that are not happy about losing the 1.5x sensor, I read where one even said he nortgaged his house to buy as many D2Xs as he could before they were gone.
So the conclusion I have reached at the current time is...
Nikon has created a camera that is a Jack of all trades, but master of none.
I am unable to find any full res shots from the D3 online, but I have a few that were given to me( and since I didnt take them I am not posting them because of Copy Rite). I cant speak deffinitively on the D3s ISO performance. But I will post a link to a full res D300 6400 ISO shot. Its not the best shot the Camera may be capable of, I can say thet the 1D3 retains much nore detail at ISO 6400. SO for now the D300 seems to be more hype than substance.
This is a large file so it will take time for it to downlaod...
D300 ISO 6400 #1
D300 ISO 6400 #2
And jsut fro a comparison...
1D3 ISO 6400
The 1D3 is a controlled test, but I am sure others may have samples to post, and if not I will try and take some to post myself. I usually dont shot above ISO 800, but I will try and get some 6400s.