I was running FSX with 4GB of DDR3 PC3-10700, the same modules as you and had no problems, occasional reloading of textures in a busy cockpit using high detail but only after being on an exterior camera.

I have however bought 2 more modules so I now have 8GB but I didn't have to, installed last week but not had time to try them out, my betting is I don't notice any problems and forget I have 8GB in now.

Ps RAM is cheap. :)