The superior high ISO/low noise would seem to be a huge plus on the side of the D4 over the lens. The question is though, with regard to your sports shooting, how close do you get for each. That's important when trying to decide if going from 200mm to 300mm is more meaningful than a better ISO/noise camera.
For my sports shooting outside, for soccer and football I'm usually on the sideline toward one of the endlines, or at the end, and I'm usually shooting with the D4/500mm and the D700/24-70mm. From time to time I might use other lenses on the D700 such as a fisheye for some interesting shots. For baseball, I'm typically using my 80-400mm on the D4 (soon to be the 200-400mm as I'm in the market for one at this point) and the 24-70mm on the D700. For inside sports such as hockey and basketball, the D4 has the 70-200mm and the D700 the 24-70mm. The thing is, I don't know where you get to go to shoot.
So, you need to analyze which would be more productive for you, more magnification, or less noise at high ISO.