I can fly me ARC 630 (4.3 projected) hybrid-foil in 24kts up to 40-45 kts. The highest winds I've ridden were 39kts. I use the smallest bar to prevent extremely quick turns of the kite and the speeds can get incredible. It definitely requires an extra mode of kite-attention, riding in winds this high, when you're so used to the large, light-wind kites moving slowly. However, by the middle of the session, I'm riding much more comfortably, and in control.
The ARC 630 absolutely rocks in high winds with incredible depower that will allow me to probably ride in 50 kts wind (controlled, but at the extreme range). The advantage lies in the rear attachment points. The further forward you move them, the more depower you get, and actually get faster turning, but since the ARC flies off front lines, the rears are slack so the turning can be easily adjusted by sheeting the bar out a bit....a great feature unlike inflatos. Also, the ARC's auto zenith tendency helps when you wipe out. Let the bar go and the kite rises to zenith and waits for you.