That would depend on the oil, and if your changing jetting, 40:1 runs leaner then 50:1, so depending on elevation and air temp, however a good synthetic oil can go to 100:1 safely,
i run all my 2strokes on amsoil dominator, at 50:1. i've not blown one up yet, chain saws, leaf blowers, tillers, dirtbikes, they all get 50:1,