Have read some good stuff on the Sigma 35 1.4...as well as the Nikon's 35 1.4G. Here is a review on the 35 incase you have not seen it yet.
If the 35mm focal length is that you are after then I would give careful consideration between the two. I for one lean on the Nikon side.
With all that said, I second msoto's recommendation on the 24 1.4G and the 85 1.8G. Here is a picture I took this past week with my 24 1.4G. This was hand held @ ISO 10,000 and is right out of my D4, hence no post processing. Needless to say, the setting was very, very dark and the result with this lens is mind blowing.
D4 24 1.4G 1/30 ISO 10000 @ f/3.5
Lastly, I happy to hear you are holding on to your 24-70 2.8...it is an Awesome lens that is always with me.