Over clocked CPU to 4.5
Nvidia Inspector Right setting
FSX.cfg tweaks
All of above with GTX660 TI can give you a very good performance
Please search the you tube for some FSX videos match your rig E: FSX i5 3570k.Watch the video and read the computer specs and you may find something match your specs So you can judge the performance of your CPU on different GPU"s
As long as you know English So you've got Avsim.Get to the hardware sections and read , you're gonna find tons and tons of of valuable information
I am gonna put a link to a blog of one of the best guys in FSX Hardware and tweaks(Kosta). He is a supper star in avsim. read the article on the link. It's gonna help you a lot
FSX/P3D Software and Hardware Guide | Kostas Flight Simulation World