1) Switching the dual AP off in high speed flight will not cause any awful response. Could the Charles Lindburghs who think so just try it to see what happens?
Suggest you inquire about a C++ operated by a large US based company in Australia a year ago.
Crews were PBI trained and current, but when the AFCS failed, the aerobatic airframe was "Overstressed" in the recovery efforts.
Took two weeks of inspections to get the airframe flying again.