Ther are two issues at play. The first is the FPS and the second is the buffer. If I recall correctly the D200 buffer is spec'd for 21 RAW frames whereas the D800 is 17 for FX. So, the D800 will shoot slightly less shots before you have to wait. The D800 can probably write to the card faster (assuming an appropriatly fast card) but of course the files are bigger so the two are probably comparable. Of course, in DX mode the FPS are higher and the files are smaller (so the buffer is effectively larger). But I don't think I would be buying a D800 to use primarily as a DX camera. The FPS is a matter of the one's shooting style and sport. If you are trying to get that "moment" (like when a bat hits a ball) its more about anticipation. But sometimes there are unpredictable events (bicycle crashes) where you just fire away and sort it out later. Personally, I find buffer size and flush speed to be the more important of the two. The non-existent D400 seems to be a better fit for your needs. If you want something now, maybe consider a used D3. It will get you the low light performance(same sensor as D700) with a nice FPS and buffer. Being two cameras back, the D3 should now be pretty well priced.