Ask this CASA guru for WRITTEN confirmation of this OPINION.
It is in writing, in a letter attached to the most recent Vic RAPAC minutes.
We are not talking about a 747 or even a King Air where you probably do have performance data for every takeoff. The reality is, smaller aircraft are operated outside the parameters of the performance charts all the time, by necessity.
The C172 performance data goes to a density altitude of something like 12,000'. Why is it OK to operate at Mt Hotham at 35C, but not Mildura at 43C?
Density altitude was part of the PPL theory. You can in fact predict the effects with reasonable accuracy. CASA actually do that in the declared density charts. Maybe you just need to break the OAT and use the declared density?
The letter from CASA is actually claiming that the ranges specified in the performance charts forms part of the aircraft limitations. Which also suggests that the aircraft must be grounded below 0C.