Chris Scott;
Belatedly realising the problem, the crew select turbulence-penetration Mach (stated to be M0.76 − that's good for an A320 but I don't have a figure for the A330).
The Airbus recommended turbulence penetration speed for the A330-200 at FL350 is M0.80 in ISA conditions; TAT -54.1°C. The forecast temp at FL350 was -46°C and probably rose considerably, so the -40C they mentioned was still a bit "low"!
mm43