Update We are keeping the D600. I will not be "upgrading" until the D500 or D900 comes out. I finally got it "dialed in". So, it is performing very well. And it fit my wife's hand. So, my second shooter will be using it.
As for frame rate, (I shoot fine JPEGs) both the D800 and D600 show 5fps as the max in the settings. Perhaps. the D600 is actually faster but I shoot at 4fps anyway.
As for file size, to bad you cannot choose medium for the RAW images.