I know about the FPS v sensor size. My boss' 7D is 18mp, however it's a crop-sensor camera. A trade-off I suppose. My comment was just that it's noticeable, even with my D200 @ 10mp.
I shoot rodeo stuff, and have able to get about 85% of what I need with my D200. Her 7D got me some of the shots between the shots my D200 would get, and that would hold true with the D600 as well.
I'm not of the opinion, yet anyway, that this camera will be too "slow"..it was just different. I have some horse show work coming up this weekend which will let me know, for sure, whether or not this camera will work for me. If it doesn't, then I work to save the difference between what I've got saved and what a D3s will cost. I know the D3s will work for what I want, just hoping not to spend $1,500 more than I have to.