When shooting in the low light conditions you've mentioned, what are your camera settings? It is my opinion that the D4 is not a huge upgrade from the D3S. In low light conditions I generally start with the following settings:
AFC-9 Auto-ISO SPOT Metering Manual mode with a minimum shutter speed of 1/160 I may add +.7 to +1.00 exposure depending on the situation
If I was going to use my 85mm 1.4G my aperture would be anywhere from 1.8-2.0. Again, these are the general settings I tend to use with both my D800 & D4.