You're making some tradeoffs and need to decide which is more important.
The D3s is probably going to be a half stop better than the D800 in terms of high ISO performance. The D800 will be around the same as the D700 - possibly a little better. And at high ISO levels you loose some of the color and dynamic range advantages. Both D3s and D800 are fine to ISO 1600. At web sized prints or 8x10 and smaller the noise will be very hard to see even at ISO 3200. I have published images with the D7000 at ISO 1600 and the D800 has the same sensor but the added benefit of downsizing a larger image. Downsizing is worth about 1.5 stops, so for the web and 8x10 prints you should have usable ISO 4800 or more.
The color rendition of the D800 is going to be better than the D3s. With both there is a dropoff with increased ISO.
Dynamic range is significantly better with the D800 than the D3s. Again - there is a dropoff with higher ISO levels on both cameras.
AF is better on the D800 than the D3s.
Shooting style will drive the importance of frame rate - the D3s is faster but the D800 is still pretty good.
Neither is a bad choice. If high ISO is your ultimate goal, the D4 is the best option but again there are tradeoffs.