I did it.
I had a bunch of FX lenses already, so the hit wasn't so hard.
The D750 feels much better in the hand because of the deeper grip, the image quality is great, focusing is fast, higher ISOs are great. What do you want to know really?
The only negative so far is that because the D7100 is DX the focus points are more spread over the frame than the D750 which has them bunched half way between the D810 and the D610. I only use centre point so it's not an issue for me.