Juliet, As far as I remember form the old aircraft the temperature limit quoted was the same, only it was referenced via sea level ISA +35C instead of being quoted as an OAT.
Piltdown Man, I would also hope that anybody who can authorise me to operate outside the aircraft limitations will have the all the answers, and more - but I don't think they have and if they do they're not letting on. Hence more than an idle curiosity on my part.
Mad (Flt) Scientist, Yup, increased failure rates are expected, but this is due to a number of other factors as well such as sand/dust ingress. The temp limits of individual 'boxes' and displays range upwards from 70degC - which does require flight deck/cabin cooling before power up occasionally as it gets far hotter in than out! (Normaly just a case of opening doors/hatches/escapes etc)
The performance of the aircraft can be conservatively predicted by using more restrictive comparables - Kabul at 6000ft amsl in +49degC is 'legal' and has valid perf data, whereas Iraq at sea level and +54degC is 'illegal' as it breaks that temperature limit of +49C although I would expect better performance at the latter.
Which brings me back to - does anyone know why the +49/50degC limit? Perhaps it is just that no-one expected the aircraft to fly in temps above this, an assumption being proven wrong now!