System Hardware Upgrade

I started playing SWS but unfortunately I'm getting occasional stutters and a lot of crashing issues where the game freezes for 10 to 15 seconds and then crashes to the desktop.  Also, my system is a little behind the times so I am upgrading some of its components based on what EA says are the minimum/recommended requirements.  I am currently upgrading my RAM to 16GB (that's the max I can do for my motherboard unfortunately) but now I am thinking about either the CPU or the Video Card.  I currently have an Intel i5 and a GeForce GTX 660.  The question I have is, if I had to choose one of these to upgrade, which one would give me the biggest bang for the buck, the CPU or video card?  I will upgrade both if need be but I'd like to go one at a time.  So, given my freezing/crashing issues, which one do you think would most likely resolve most (if not all) of those issues?