Almost everything has already been said, this is rather a sum up:
Your current rig seems to be a balanced example of the top quarter of modern gaming rigs. If you want to improve performance, a total rebuild would be needed except for the RAM sticks! Definitely not in the $200 range, you already are in the range where the prices of frames rise exponentially.
If you don't get great frame rates in AH with that, it isn't in the lack of power, it's in where it's used. In AH, you should be able to max everything with a couple of exceptions: Leave AA and Environment mapping to "none". At least that works for me with a resolution of 2560*1600 with a dual core E8500@3.16 GHz, 8 GB ddr2@800 and Radeon HD 6970 2 GB gddr5. 30 processes running on Windows 7 64 bit...
I wouldn't even invest into an SSD since it does absolutely nothing for frame rates. It makes things load faster, though, so if you really are in a hurry it would get you into the virtual skies a minute sooner starting from pushing the power button. Personally, I'm using that minute to get my gaming gear into position. BaldEagl has a point in suggesting saving the money or taking her out to dinner. Split the budget and do both! If your GF still wants to get you something to improve your gaming, a screen cleaning kit is very useful to get rid of extra dots on the screen.