Your card should be able to play BC2 at the "High" settings. I don't play either of those games to give you advise on the exact setting to try. Have you tried the new Nvidia 258.98 drivers yet? NVIDIA DRIVERS 258.96 WHQL
The biggest issue I see with your system is the dual-core cpu. Most newer game will utilize 4 cores if there available and it helps. Plus the extra cpu power helps the video card develop more video bandwidth. Even with your cpu at 4GHz I think it's causing a bottleneck. An i5 750 would make a believer out of you. I went from a QX9650 to my i7 920 and the saying the difference was noticeable is an understatement.
Some features of DX11 will cause a lose of frames. That happens with every new version of DX and the new features that come with it. If the game your playing has a option (DX11) for Advanced Depth of Field you should try disabling it as it will impact the system pretty harshly.