The low light (IQ) performance of the D700 is the same as the D3. So if you like the D3 performance and the D800 is slightly better than the D700 and thus D3, then you should love the D800.
Its speculative until we see a number of images from the D800 under varying conditions. There will likely be a D400 and it may be better in low light than the D800 and be geared to sports/low light for users who cannot afford the D4. But if you are not in a hurry, you can wait or buy the best option for you that is available now.