lot of people choose the Common sense approach of extrapolating data for higher temps
.. if you don't have the engine data sets, in particular, you have not much idea at all of what happens at higher OATs other than presumptions based on general principles. Extrapolation into the higher OATs is not a routinely good idea, I suggest.
how are you certain that beyond the 40 degrees performance data stated in your POH
I would think one would have very little idea of what might happen.
Re the W&B considerations, I presume you are referring to the usual sloping limit lines on the weight x CG envelope ? They will only be first order there and, if one uses the weight x moment presentation, quadratic .. but, for a computer solution, why would you bother with the latter ? Not a big problem, I would have thought ?