When adding text to your video, keep in mind that bitmap (pixel-based) images take less time to render than vector (mathematically-based) graphics.
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So what does this mean for you? If you create your graphics in FCP using the text tool, don't render the sequence with that text element in the timeline. Instead, make a Freeze Frame (shift-n) of the text and place that in the timeline.
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This works best for lower thirds and static text. If you need a scroll, using a photoshop text file with an alpha (transparent) channel is best, and then keyframe the center in the motion tab.
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another note: changing the center in the motion tab requires less rendering than moving the location of the clip using the wireframe.
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There are a lot of things you can do to speed up render time by using different file types. Also, if you graphic images in your timeline, use some type of graphic converter, be it Photoshop or Preview (on the Mac) or whatever, to scale your photos to 720x534 before you place them in the timeline. Scaling pics in FCP takes a lot of power and render time as well as hard drive space.