Upload & Sell: On
Let me say first of all that I own the D3s. It is without question the finest camera I have ever owned or shot. Fast. Amazing color. Flawless AF system. I can't imagine how the D4 could be any better.
However, there is a caveat. Almost everything I shoot is sports. I shoot a lot of images at ISO 12,800 -- and the D3s is spectacular. However, some noise is acceptable in sports photography. I don't know that the same level of noise would be acceptable for wedding photos.
My advice? Ask yourself this question. Realistically, how often do you need to shoot at those elevated ISO settings. Only you can answer the question about how many really, really dark churches and ceremonies you shoot.
If you don't need the extremely high ISO's, jump on a low mileage D3. It is a spectacular camera. Financially, it is no problem to buy a very low shutter count D3 for $2,000. With the extra $1,500, buy Nikon's 24-70 f/2.8. That makes an amazing wedding rig -- and I think after being on the D90, you will feel like you died and went to heaven. Your results will show a dramatic difference in image quality -- and the jump from the DX to FX on your camera will blow your socks off.
Just my two cents....