Based on the DPreview's studio test scene for the usable high ISO range from 6400 to 25600 I think D750 is up there with the top guys, if not better (see attached photos).
Everything I have read indicates that the D750 handles low light very well. It's a moving target since with each new camera release, technology moves forward. I don't think anyone would be unhappy with the high ISO capabilities of the D750, though.