Last time I passed PPL my wing sees only air density, my internal combustion engine only sees air density. The charts are there to help the pilot make interpretations easier. Just because the company calculations stop at 40C does not mean that is a limitation. If there is a pressure altitude up to 8000ft that means you have density altitude to 8000ft USE IT! and tell CASA where to bloody go if they ever try this on you!
Among a sea of bush lawyers (and a couple of real ones) at least someone is on the ball and knows their stuff.