I accidentally found a hack to boost frame rate performance in airplanes equipped with secondary instrument screens. This is how you do it: Start a flight, then pause the flight, open the secondary instrument screens and minimize it or move it to the second monitor if you have one, then you will see frame rates jump up tremendously and the flights become very smooth.
I do not know why but suspect it might has something to do with multithreading in a multiple core processor. I use AMD processor and GPU and use adrenaline overlay to monitor my frame rates, not the developer console. I also use Direct 12(Beta).
Please post your experience and potential explanation.