Save yourself the rental fee. Just get the D600. The D700 wil give you higher FPS. That's about the only advantage I can think of. If you want to see some basketball images shot with the D600, just head to my website.
The filenames will tell you the D600 vs D3s images. Hit slideshow to see the images a bit larger.
>I've been on the fence about upgrading from my D300 to a D600 >or a low shutter count D700. I'm going to rent the D600 and >give it a workout at some high school basketball later this >week. I really like the D700 size body but am reluctant to >buy the older tech.