"Ultimate CPU/GPU combo"? Of course that's not needed, but having good parts helps. You have one of the best quad core CPUs that AMD makes. FSX needs CPU power so of course you'll do alright. Ever see anyone try to play it with a lower end dual core? How is it false if you bought one of the best?
The 5670 isn't a bad GPU either. I'm guessing your playing at 1440x900, or 1680x1050. I'll call BS if you have the 5670 doing that at 1080.