Hello Chris;
Just some comments on the trop; - the A330 rides the transition quite well even though, as you say, the ride can be rough.
I would say that temperature variations aren't wide enough to cause concern in terms of being too warm.
The optimum altitude and maximum altitude charts for M0.80 and M0.82 are below.
ISA+20 would not be a problem at FL350, 205T; the charts are for a cg of 37.0% but I believe a cg of 39.5% would not significantly affect operation in ISA+20 conditions.
The 'n' curve, (1.4g & 1.3g) indicate buffet margin. There are no bleed corrections for optimum altitudes but max operating alts for ISA+20 are reduced by: Engine Anti-ice only, 800'; Airframe and Engine A/I, 1900'.
None of this, by itself is a big thing. This is the stuff of normal cruise, and the airplane is a long way from the boundaries by planning and good flight management.
In reference to the reduced altitudes if antice protection is 'on', by "reduced" I am thinking that the airplane would probably stay at altitude if established there already but descent may be required if it warms up.
In other words, this kind of reduction doesn't meant the airplane is anywhere near "coffin corner" but astute crews may descend for slighly lower fuel flows.
Speed would not be a problem in most cases but if it warms up, a very slow bleeding off may occur - nothing dramatic that any crew wouldn't be able to plan for and determine a course of action.
Though the caveat is always "anything's possible", we have to bear in mind that ISA+20 is rare, higher even more rare, and they would have known about this variation from the flight plan.
Fuel load, cruise altitude selections, loading and routes would have been taken into consideration - it's standard work.
PJ2
