The best comparison I can come up with is using Sam Houghton Challenge results from last year:
46km and 1400m of ascent.
I’d call that a fairly typical day ride in the hills, but trying to be quick.
The fastest guy I’ve ridden with took about 3 hours = 15.3 kph (and I think he’s now competing internationally at bike orienteering stuff)
The rest of us mere mortal club riders were strung out between 4 hours and 4:45 so 11.5 kph to 9.7 kph
On a social ride over the same distance & ascents, I’d expect to add at least an hour to that for chitchat, eating and generally slower pace, so that would be 8 kph absolute max.
Go to somewhere steep and techy though and I’d not feel too ashamed if I’d halved that again, 4 kph !!!