I owned the D750 for two and a half years and yes the IQ on the D750 is superior.
AF selection with the D-Pad is faster than the X-T2 joystick as well.
The biggest thing for me is that when shooting ISO 12,800 in actual low light and low shutter speed, the D750 still has a lot of detail in the eyes. The X-T2 doesn't retain much if any. You can't even tell what colour the eyes are half the time cause it is just all shadow and mush.
You could pull the shadows up till the cows come home on the D750 but not so much on the X-T2. On the X-T2, you can recover the highlights about 1/2 stop or so better than the D750.
The closest lens on the Fuji side that will give you a FF look is the 56mm f/1.2.
The D750 jpegs weren't very good. The D500 has a much better jpeg engine. The Fujifilm jpegs are good but has weird mid ISO (400-3,200) noise and can sometimes look very crunchy.
But saying all that, I still sold off my D750, grip, Nikkor 24-70mm G f/2.8, Sigma Art 50mm f/1.4 and SB-910 for the X-T2, grip, 56mm f/1.2, 23mm f/1.4, and 35mm f/2.
The weight wasn't so much the factor but the size was. I started not wanting to take it out of the bag even though I took it out with me.
I wish Adobe would get its act together and improve LR for the Fujifilm sensors so we can really see the potential of its raw files.
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