Arlo i would recommend holding off from buying anythink until aces high 2 comes out.
When aces high 2 does come out. Take your local computer down to a computer store, and say that your intrested in buying hardware off them. But you need hardware to actualy make the game play good. Show them the game, and the frame rates. Then ask them what equipment may or maynot help in the frame rate department. Normaly i found that computer stores are more than happy to swap ram and video cards in and out of your system, finding the best configuration. It saves you money and also it makes them a profit.
The solution above is the best choice i think. Firstly they will have more understanding of your system than you do and can simply point out what needs to be replaced. If the computer store doesnt want to help you out, take your businesses elsewere. Also, its good to show them the cash that you are expecting to puchase the hardware for. This will also add a bonus to your side, because they wont think your a con man!
Well i used this proccess, but i also knew the people at the computer store, so that was also a bonus.