I did some digging and ı found a solution (other than just running the Game'in DX9 mode)
In \Documents\My Games\Far Cry 3\GamerProfile.xml there's a setting called D3D11MULTithreadedrendering="0". GO ahead and set that to 1. ı'm now able to Max it out with no more slowdowns and much higher CPU/GPU usage.
Edit: If you're experiencing instability with this option, restricting the Game to 4 physical CPU cores also yields significant performance improvements.
You can also set ıronsighttogglemode="0" to 1 if you don't like having to hold rmb to aim down sights.
Hope this post helps someone.
Hocam bu da olmazsa ben pas geçiyorum.