We have had the main UFH turned down to 14C as that is enough for rooms we don't normally occupy. The upstairs heating has been almost entirely off. because the bedroom we use has wood burner, and we only run upstairs heat for when we want hot bathrooms.
we have an Aga on an internal wall between the kitchen and the dining room.
The kitchen is at 18-20C. The dining room is at 14C. The living room is beyond that and is also at 14C. Dining and living room are semi-open plan with a large passage between them about 7ft wide.
The bedroom above the kitchen is a 16-18C.
The bedroom above the dining room (only two outside walls, and a lot of leakage via the door and wall; from the 'hot bedroom' is at 14C.
The bedroom above the living room is at 12C.
What surprises me is that even with a carpet, insulation, and some insulation board, the interface between downstairs and upstairs seems sufficiently leaky to keep upstairs at really almost inhabitable temperatures relying solely on the ground floor UFH.
I thought I would pass this on, a those who say 'I like my bedroom 2C cooler than living space' can more or less (if the floors are not massively insulated between), get that sort of differential with downstairs heating only, if the insulation elsewhere is up to snuff.