If I have a hexacore I7 that is 4GHz and a 550ti GPU, why would the game run slowly when I have such a great processor
Graphics cards are the driving force when using programs that have to display many images per second. Your processor only processes things in 1's and 0's while your GPU interprets the 1's and 0's it gets from the CPU and translates them to images that are displayed on your monitor. Your i7 is basically sending 1's and 0's faster than the 550ti you have can make them into images. This is what we call bottlenecking. Your GPU is limiting the performance of the i7. If you had a more powerful GPU like a GTX 760, the higher amount of image processors that the 760 has would be able to take the 1's and 0's and make them into images much much faster, taking the full advantage of the i7's immense power.
Upgrading your GPU will get you way more FPS because of this. I hope this helps!