The two factors that most affect your rendering as well as your encoding speed are:
1) The power of your processor. So, yes, indeed upgrading to a quad core processor would make a significant difference in your performance. Your graphics card and RAM have no real effect on your rendering speed.
2) The format and resolution of your video.
The resolution, for obvious reasons. It takes longer to render 1.5 million pixels (hi-def) than it does 345,000 pixels (standard def video).
But the format can also make a difference. If you're using video from a non-standard source, like a still camera or a Flip camera, the program has to decode the video in addition to re-rendering it.
And AVCHD video, because it's so highly compressed, takes the longest of all to render.
In other words, video from a miniDV camcorder should render rather quickly after you add an effect to it -- which video from an AVCHD camcorder will take considerably more time.
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Export and Rendering speed can also be affected by one's I/O sub-system, i.e. your HDD's (Hard Disk Drives), their speed, amount of free space, the controller type and how you have these HDD's allocated.
With the exception of AVCHD, which Steve mentions, having separate physical HDD's (not partitions - logical drives), will speed things up greatly, as all operations on the computer, access to the OS, the program, the media files and then outputting from the program, will be spread over several HDD's. If you only have one physical HDD, everything has to flow through one "pipeline," and this adds significant time to the processes. Having partitions will slow things down even more, and can even cause hangs, because the OS "thinks" that it has multiple HDD's to use, but only has one. It cannot understand what's taking so long, and grows impatient.
With AVCHD, the CPU is used much more than even the I/O sub-system, and becomes the most important link in the chain.
Good luck, and let us know all about your HDD's, their number, size, speed, controller type, say SATA II, and how you have these allocated.