FCP for me, turn on the Unlimited real time rendering at it should be fine, most people seem to miss this option. It will only become slow it you are really hammering it with 8+ effects on each clip.

Although I don't do weddings, I've produced several 2 hour multi camera performance videos, and rendering and exporting weren't really an issue, this includes colour grading through the duration, the occasional luma/chroma key, and a whole load of cross dissolves, as well as motion graphics and titles.

If exporting in full native quality from FCP is surprisingly quick (5 minutes can be exporting in a matter of seconds). rendering obviously depends on what you've done to the video, but I don't think the above 2 hour projects took any longer than real time to render on a single processor. (256MB Gfx) Encoding for the dvd took longer, but was still done well within hours rather than days/over night