If you own both, you tell us?
All I can say is I've had the urge for FF again recently, but every time I use the middle of the road APSC Fuji, and process the images, I'm continuously impressed. Then I wonder [again] what more do 'I' need. What you 'need' may well be very different, and I don't think anyone can really tell you one way or the other.
I shot a party today with the X-H1, no flash, and only used a 16mm, set it to 1/250th and auto ISO - flicked between 1.4 and 2.8 all day, never even checked to see what the ISO was doing. Turned out a lot of the images were between 2500 and 6400 and in post I really felt I didn't need to tinker with much, let alone the NR. What would a FFML have offered me over this? Possibly a cleaner image at the same ISO, but after showing people [who don't pixel peep] the images, not one person noticed any noise or suggested the DOF could have been shallower .... I also didn't miss focus on any images - and a lot of it was shooting dance floor [Christmas party]
Price. Lenses maybe? not feeling the need to bung GM lenses on because you're using a higher end body.