>I think you'll find your lens' center performance will be very similar to what you've come to expect on your D300. The D800's pixels aren't all that much smaller after all. I think the people mainly raising this concern are moving from D700 or D3(s) which has much larger pixels than either of these cameras. Corner performance is a different story, however if auto racing is your main subject, I'm guessing corner performance isn't critical to you.
Please, let's focus on this point. My main concern isn't "reach", 200 or 300mm.
My main question is about performance (sharpness, detail, noise, etc) in the center, but also in the corners. What do you think about will be be the behaviour of my set of lens (that, normally, I won't change in the next months/years) with the D800?