Originally Posted by
RustBeltRaw
I agree with the gents suggesting that a D4 or 1DX is overkill. If you have that kind of coin available, I'd look very closely at a Nikon D3 or D3x or Canon 1D mkIV and a 200mm (f2.0 or f4.0) or 300mm (f2.8 or f4.0) prime lens with a 1.4x teleconverter. Strongly suspect that would give you better results across the board than upgrading the body alone.
For whatever it's worth, I tried a 1DX in the camera store alongside my recently-purchased, 6-year old 1D mkIII. It's a speed freak, a low-light marvel, and a pleasure to shoot, but in my opinion, not worth $5,600 more than my 1D mkIII (paid $1,050 used). Makes more sense for high-end concert or indoor action photography than outdoor work.