I am glad to know that you have found the D800 to perform well at ISO 3200. I thought that it was effectively pretty much limited to 1600; however, I realize that what is "acceptable" is subjective. 1600 is the maximum ISO for my D200, and far better to leave it at 800.
It is helpful to have the benefit of your experience. Permit me one more question: In what way do you find the D600 to be superior to the D800 for sports work?