What size wing? My max so far has been around 30kt, maybe 35kt gusts, with a 4m. It does get a little intense on the gusts, holding it down, plus the chop gets difficult to keep foil in the water so have to slow down a lot.
The wing would whip around violently on leash too, not sure if enough to cause a shoulder injury, but having leash attached to belt may be safer. And some funny behaviour with the foil, would get pushed on its side just by wind force, took a fair bit of force to get the board to stay flat.
All in all, it kind of crossed out of "fun" into survival mode, doable, but on alert-mode vs relaxed wave riding. But TBH when it's 40kt and on a 5m kite or less, I am not exactly relaxed either!