Thanks for that advice but if performance is hindered how do I get it back?
Turning off each and every Compatibility setting. Some of them might not be easy to check for, because they are in the registry, at the following key:
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
Remove everything related to FSX.EXE, if you have any. The GSX/Addon Manager installer also clears them up, which is why some users reports of problems gone when reinstalling.