I shoot the D800 and my raw file size ranges from 38-48 mb right out of the camera. I processed some images yesterday as medium jpegs (quality 10 in image processing out of bridge) my files range from 3-6 mb at 300 ppi.
I also came from a D300 and the raw file size is quite a jump. It works for me, but it's way more than most people need or want. As far as the D800 itself as far as function and quality of picture I love it. I warn you there will be a learning curve shooting with it and shooting sports with it will definitely take some time to adjust to.