Instructions
Open ̶0;FSX,̶1; and then select any mission or scenario.
Wait for the environment to load fully. Displayed frame rates are meaningless until the game is actually rendering environments and objects.
Press ̶0;Shift-Z̶1; twice to turn on the frame rate display. Press ̶0;Shift-Z̶1; again to display other performance information, and press it one last time to hide the display.