The chart ending at 40 deg's C is there for a reason; either flight testing was stopped, or the aircraft performance didn't warrant any further certification, either way be very careful if you decide to interpolate or extrapolate because if there is a reason for the insurance companies or CAA/FAA to get involved you won't have a leg to stand on.
As +TSRA says above "there is never, ever, a reason that you HAVE to go flying" especially for pleasure.