I thought you basically said once the system swaps from IAS to MACH forget the IAS and fly .82 as the turb penetration speed?
This is not correct for all ops. Normal cruise in the ER as you know is around FL300 initially at about .82 to .83 indicating about 300 to 310 KIAS ( from memory) now in this case should you encounter turb you most definately don't fly at .82 and disregard 280 KIAS. You slow below .82 to 280 or min man +15.