Picture above at ISO 3200 here 1/250s.
I had the pleasure to test the Fuji GFX today with the 63mm f2.8.
All shots are jpg done at f2.8, no tripod, in street setting. So no ideal conditions, but might help to see if it fits your bill if you are not shooting in controled conditions. For street there might be cheaper and better options anyway.
AF was hunting a bit, MF is really not nice with this focus by wire. Zooming into 100% in the EVF is well implemented and it was easy to focus manually.
This shot above at ISO 12800. Manual focus on the girls eyes and hit.
The files here are low res, all my page can handle! Sorry about that. I intended to show you the overall look of the images. All images are in focus and reasonably sharp view at 100% even people are moving and iso is high. Certainly at iso 100 with flash freeze in the studio, you will get more detail.