If you would use the system only for FSX, you should get an faster processor, around 8gb ram, and a good GPU (Graphic card)
If you would use it for other games such as battlefield 3, 4 later these options are fine for you.
I would go for:
Cpu: Intel i5 or i7, depends on your budget. If you want to overclock you should go for the K series (Ie i5 2500k) and some cooling on it other than the stock cooler.
Ram: 12GB.
GPU: Gtx670.
Motherboard: ??, imo it doesnt really matter as long as it has some pci-e slots, and some nice features such as usb3, eSata. This all depends on your budget again. Personally i use a H61-M US by asrock an it works perfectly fine for me.
HDD: I would go for an 750 HDD, and an nice SSD of around 128gb. To install your windows on and maybe even FSX. Ssd's are alot faster than hdd's
Also you should say an budget here as it's easier for us to tell you what would be good. Also telling where you would use it for would be useful aswell :3
There are plenty of sites where you can customize your PC desktop and they will build it for you.