My guess is that CASA partly, at least, bases their opinion on CAO 20.7.4 which changes the scope of this discussion.
e.g. " An aeroplane must not take off at a weight in excess of the least of the weights determined in accordance with subparagraphs (a) to (d):
(a) a weight at which the take-off distance required under subsection 6 for the pressure height, temperature, runway slope (if in excess of 1%) and wind component along the runway, is equal to or less than the take-off distance available in the direction of take-off. Approved declared conditions may be used instead of actual pressure height and temperature ..." etc.
i.e. if the performance information stops at 40 deg C (per FAR 23) then how can the pilot show compliance with CASA performance requirements at higher temps .....