fsx = a huge no. FSX loves cpu cores, more more more. LoL
edit - dont get me wrong, an I3 will work but the fx6300 for nearly the same price would fair better esp since its overclockable.
FSX's main process uses only one core, so a fast overclockable cpu is recommended. The other cores get used less but FSX will use all that you have available. There are guides available on how to set the cfg file for the number of cores you have.