If you have a good PC with a good video card, you should be able to play most games full speed at reasonable resolution and graphics quality. If you can not, then read on.
1) Determine the bottleneck if turning on the real time statistics in your emulator. Both 1964 and PJ64 support such a thing. Your emulator will then show the CPU percentage usages on the status bar.
Most CPU should be used by video plugin and emlator r4300i core.
2) Using higher speed counter if the r4300i is using the most CPU power. Almost all emulators are supporting counter speed change. For 1964, you can use 4 or 5 instead of the default value 2.
3) Using a faster emulator instead of your current one.
4) Using Azimer HLE audio plugin 0.13b or 0.30(old) instead of Jabo LLE audio plugin
5) Disable RSP.dll or config RSP to pass both audio and video to audio plugin and video plugin.
6) Using lower resolution in your video card. Using 640x480 instead of 1280x1024, you could get 100% speed up.
7) Using DirectX instead of OpenGL, you can usually get over 30% speed up.
8) Using 16 bit color instead of 32 bit color. You can get 10% speed up.
9) Try different video plugins, could make big difference.
Enjoy your game.