With an i7 you are most likely suffering (the most) from your older GPU. 2GB of ram is pretty low nowadays. If you install MSI afterburner you can monitor your GPU usage and GPU RAM usage to see if its a bottleneck.
For example, I run the game with an i5 3570k @ 4.4GHz, 980ti Hybrid, 16GB 1866MHz RAM, OS and game on an SSD and I BARLEY hit 60 FPS on a lightly filled map using a customized medium setting. I only gain about 2-6 FPS by changing from my i5 to a xeon 1231 v3, but my CPU load drops from 98% to 85%. The game is simply not super optimized, but is definitly CPU bound on mid level machines, and GPU bound on low end machines.