Honestly, having had a D800 since June and a D700 for 2 years prior I'd go with the D700 for indoor sports. Mostly for frame rate and similar low light level performance. Cheaper, too. And you won't have to worry about file size.
I've shot some football recently with the D800. Made me want to go running back to a D700 or even a D300. Not saying it can't be done -- it most certainly can be. Just that the D800 and D600 are not your only (best) choices.
If you're selling pics, I'd definitely consider a D3 or D3s before going with a D600/800 for sports.