I think if you get a new D800, you should be fine on the focus issue. Make sure you buy it from someone with a good return policy, just in case. If you buy from a physical store, test it before you ake it home.
Here is what I think you will find regarding the D800, D700 and D300.
The D800 will turn out to be great for tripod shots and when the light is good and you want to handhold. You won't be crazy about it for action photography, especially in low light. But you will love it's dynamic range adn detail, when you want it.
The D700 will be great for carry around, casual photography, and lower light situation. You will appreciate it "forgivingness", and also the fact that you don't always want a 40-50MB file.
The D300 will become the orphan because if it's lack of dynamic range and mediocre (by current standards) performance at higher ISO. You might miss the DX crop, so think about a D7100. Great DR, better high ISO performance, still has 51 focus points. But too bad no 10-pin connector. (Life is trade-offs).