Just for reference (and so people don't need to guess), here is a factual (and some benachmarks) comparison of a plain 780 and a 780M (as you will see, the difference is not so small): http://gpuboss.com/gpus/GeForce-GTX-780M-vs-GeForce-GTX-780And in a different thrad at x-plane.org I wrote about the many things which need to be considered when it comes to FPS: http://forums.x-plane.org/index.php?showtopic=81150&p=864489Nevertheless ... if you are "sure", that under the exact (and this exact might be more complicated to achieve, than one might think!!!) same conditions you get extremely different results, then there might indeed be an X-Plane problem 8but one very "subtle" one, which many many others can't easily reproduce ... which make diagnosing it hard)