This one is really not too hard. You need only answer one question.
Is ISO performance at 6400 and beyond your primary consideration?
If so, buy the D3s. If not, buy the D600. The image quality in nearly every mesure of performance is higher with the D600, and ISO performance is 1/3 to 1/2 stop behind in my experience. I shoot these cameras back to back every week. That's my feeling on the matter.
>In reviving this topic, I'm contemplating the D600 or D3s. > >Currently a D200 shooter and get paid to shoot rodeo sports. I >can get about 85% of the images I need from the 6FPS that the >D200 gets, but will miss shots at times for things like barrel >racing, reining horse and roping events. Hence, the >consideration of the D3s. > >However, I also shoot these sports using single shot and >strobes (covered arena), so timing is more important than >frame rate. > >Thus, I think I can work with either for what I do there. > >Where I am on the fence is for low-light stuff. I'm looking >to market myself as a second-shooter for events, weddings, >concerts, etc., so low light and image quality are important. > >I know that 24MP doesn't necessarily mean better IQ, but you >do have more pixels to work with if you have to crop in. >Also, I know the D3s ISO goes to 12800, but you don't judge >how "fast" a car is by the numbers on the >speedometer. > >Therefore, I'm trying to figure which of the two would be >better for lower light stuff AND have better Image Quality and >those ISOs. The D600 is newer and likely benefits from >advances in technology. However, the D3s is the "king of >the hill" (or was) in low light performance. > >Thoughts? > >Given the D3s is nearly twice the price, used, as a D600, that >is another factor under consideration. > >Thanks, >Tim