which settings is the most suitable for me? (dx11)
Running the game in DX11 mode might put some strain on the video card. But the CPU will be a bottleneck to your system, I am not even sure it will run properly.
Your CPU will be a bottleneck. While your GPU is a decent mid level card, you should be able to run it on medium settings with the resolution somewhere around 760 on the lower side.
the game will run but at or below medium settings... as you have a 1gig card you should be ok for any rez up to 16/10... as your cpu may bottleneck the game you may want to run slighly higher on the gfx to offload from the cpu... your max fps wont go up by much but your minimum should go up enough to make the game playable...
also dont bother with dx11. your card doesnt have enough grunt to pull it off.
dx9 on medium settings should run fine at any resolution. I have a friend that played it at those settings on a core2 duo and a 9800 and it didnt look too choppy.