Regularly shoot boar-size game out to 70 or 80 metres with express-sighted rifles, and have made shots to ~180m or so by flipping up the 200yd leaf. One on a fast-walking pig at almost 200 with my .400 Jeffery was caught on video.
However: it depends a great deal on the sights!
I have shouldered a number of express-sighted doubles belonging to other people that I wouldn't have taken into the hunting field without serious modification if they were mine!
A correctly-sized gold bead, fairly fine, over a wide vee rear with gold or platinum centre-line or triangle should be good to well over 100 metres, up to 200 metres with a rest of some kind.
Some "traditional" sights such as the barleycorn/buckhorn are a serious handicap with my eyes and I have trouble understanding how they were ever used successfully in the field, particularly when the quarry is on the move.