given the opportunity to purchase either the nikon d3 or nikon d3x at same price which would
you choose and why??
given the opportunity to purchase either the nikon d3 or nikon d3x at same price which would
you choose and why??

Depends on what you shoot is the standard answer for this type of question. I shoot birds in New England and need a DX body for that, even with a 600 lens. Aside from that I do not shoot where high iso is required. The D3X is great for resolution and dynamic range in landscape photography. I also use it when I shoot larger birds at Bosque or in Florida. The only way it suffers for me is slower fps.
One of my friends has a D3X, it's an amazing camera. The crop mode in D3X gives you about 12 mpixel which is the same as a DX body so current DX bodies like D300 have ZERO advantage over D3X.
Maybe, you have already answered the question on FF versus cropped sensor. If you have not, that would be my first question. With the new D7000, and a more useful ISO range over the D300......it is now a more interesting discussion...........Why would you spend $7,000+ to shoot a D3X in cropped mode.
If you have settled on FF and plan on having only one camera...............I would not recommend the D3X for any kind of action work or any application requiring ISO over 400. There are exceptions, but if you primary usage is birding/wildlife where FPS, shutter speed, long lenses, often low light conditions are a consideration it is an expensive and limiting choice.
Rather, the D3, or better yet, the D3S will give you way more flexibility in field conditions..........it is my go to camera for birding.The 9 FPS is ideal for action sequences...........and there is essentially no noise through ISO 1600. ISO 3200 cleans up well with just a tad of noise reduction, and 6400 is also very usable. I typically shoot around 750-900mm (with T/C), and push the ISO to get higher SS even in better lit situations (results is more keepers!).
As stated above for static subjects, the D3X is superior in tonal range, color transition and resolution. How superior? That is another discussion.
I do not have a D3X, but I read a lot about them, and I was not aware they had better tonal range. in fact I thought that it was more or less a D300 sensor in full format. It certainly does not have the ISO range in the non-HI portion of the D3 (200-6400), since it runs only from 100-1600. In fact the D300 is 200-3200.
I really thought the D3X in crop mode was really almost a D300 (except it can shot really, really fast!).
Now if someone wants to send me one to compare.... :)
Corrected, I should have said dynamic range rather than tonal range, since they both can shoot at 14-bit raw (16,384 tones). They use different sensors. The original question was D3 or D3x. They are different cameras for different purposes, already covered in the thread.
Actually dynamic range is one of those things that still confuses me. I often here the D- cameras as being superior to the dx D--- versions. But the actual numbers are interesting. In the FWIW department, I looked up the DPReview dynamic range at base ISO for several cameras and it is surprising (looking at "usable range"):
D300 8.8 EV
D3 8.6
D3x 8.4
D300s 8.4
D700 7.8
I would have never guessed the D300 (non-S) would be at the top, as it is no where near as good at high ISO as any of the rest. To me it is very counter-intuitive that good high ISO performance does not translate into good dynamic range (even though I realize they are different things).
Of course, depends on who you ask. Here are DxO's figures for the same thing:
D3X 13.65
D3 12.23
D700 12.15
D300 12.04
D300s 11.98
D3s 11.97
Kind of flips things around.
Anyway, just for your amusement.
I don't read dpreview. Away from the numbers, I can tell you that the ability of the D3X to capture a full range of light/saturation all the way to preserving detail in the darkest shadows is significantly better than any Nikon camera I have ever used. I typically rarely shoot beyond ISO 400. Although I have seen amazing images at 1100..........There is a technical discussion on the web/Nikon site regarding the actual pixel mu size that helps explain this better than I can. At base ISO, the images are stunning.
BTW, I sold my D300s in favor of the new D7000, which I like even better for cropped sensor work.
Completely different sensor technology, different sensor pitch, different AA filter - almost nothing about it is like a D300/D300s. It is most definitely not like a D300 in crop mode. Even the pixel count is different and is 10MP in DX mode while a D300 is 12MP. Also a D300 is faster (especially with an EL-N 4 battery), as in more FPS, than a D3x in DX mode.