Hey, I happen to have the same setup as you.
I5 4670k, overclocked to 4.4, 8Gb Ram, GTX 660, Win 7 64 bit. Same.
I see from your CFG that you are running DirectX 9.
On my system with a clean install and simply the HighMem fix, FSX + Accel, I get great frame rates and no stutters even with Anti Aliasing turned on.
Adding in WOAI aircraft at 60% and a single payware or freeware airport - still no stutters.
I have since switched to DX10, but by system ran very smooth with DX9.
What else do you have installed?
Your video card should not choke this game unless you are running full AA and have a crapload of Cumulus clouds and a thunderstorm going on.