I find them to be about equal. Above ISO3200 the noise is too much for anything with fine detail. I prefer to stay below 2200.
Even then, unless I am looking for a large file, I'll use the D3s when light is a problem. I'll take that to 6400 without a care.
Here are some samples from a recent Puget Sound Nikonians shoot on a day with poor lighting. All were taken with a D800e, Sigma 150-500 OS on a monopod at f/6.3, 1/500sec. These were a sequence taken with Auto ISO on. These are 100% crops
At ISO 3600
At ISO 2200
Unfortunately, I didn't have my D3s along to provide some comparisons.