What should I upgrade to improve performance?

Hey, I love dolphin and all but it lags in games like F-Zero GX and Resident Evil 4. In Resident Evil 4, the game runs fine until I have lots of lighting sources on the screen, and F-Zero GX can't handle being run at 1080p fullscreen.

I want to buy myself something for christmas, and I'm leaning towards getting a new graphics card but I wanted the opinion of this community first.

Windows 7 x64
Intel i5 760 2.8 Ghz
XFX AMD Radeon HD 5770 1GB
Mushkin 4GB