I have tested it:
- if I press pause, the game un-pauses and camera zooms out. I get 23fps.
- if I press esc key, I get 26fps in cockpit but the game is still paused. If I press pause after that, the games un-pauses, camera zooms out and I get 23fps.
On a side note, pressing alt-tab to exit and alt-tab to enter the game gains a few FPS...