Arma III I can understand putting a load on your system, it's resource hungry and will soak up everything that you can throw at it.
But with CM, it's actually the game software that's the bottle-neck.
Your system, basically, should be running it as well as it can be run.
What's your FPS in the game we're currently playing, with model and texture options set to best and AA on?
As for Mods. I'm running high definition textures, all of Aris vehicle models. sound mods, etc.... on a system slightly more modest than yours. So theoretically you shouldn't have any issues.