Here is an observation that might help some people that get caught in mid flight with low fps...
For some reason if my fps drops to single digits (due to weather or terrain that demands more power than my PC has) switching to virtual cockpithelps a little bit, but switching to the co-pilot seat gets my framerate back almost up to normal.

I have no idea what makes the co-pilot seat perform better as almost all the info the pilot gets the co-pilot also gets. But for me it really makes a difference.