None of those options seem unreasonable, so I can see good arguments for any of them. If it was me, I'd ask myself if I need a second camera now. It sounds like you use two and the answer may be yes, in which case I'd get a D300s. But if I could wait, I'd be hoping for a D400 in the first quarter of next year. If your criterion really is the best low-light performer, I'd get a D7000, to stay with the DX sensor, although a D600 might be best for this criterion. My personal choice: wait for the D400, followed by D300s if I really needed it now. But as I said, there are good arguments for all those options, so I can see why you asked the question!