Superzooms offer convenience in focal length range for sure, but the trade offs are usually in image quality, aperture size and perhaps AF, especially when compared to an L lens that is generally regarded as a good lens. I don't shoot weddings, but I occasionally shoot low light / indoors and I'd be reluctant to use a lens that is f/6.3 wide open, especially without a flash. Outdoors in daylight might be OK, but I assume you're also shooting indoors. Performance, client satisfaction and the budget are always the qualifiers.
You've probably checked lens review sites, I'll offer a few just in case you missed them.
http://www.dpreview.com/lensreviews/This same site has various forums, including one for Canon lenses (Sigma on Canon bodies is discussed). It gets a bit rowdy, but there is some useful information and you can always post questions. This is a very active site, a search will generally turn up lots of posts. The Digital Pro forum has an occasional thread on what some wedding photogs carry & shoot, you may already be aware of this site and what others do.
The Digital Picture has side by side comparisons, sometimes the bodies are cropped sensor types, so FF corner performance is missing.
http://www.the-digital-picture.com/Revi ... &APIComp=2One more
http://www.slrgear.com/reviews/showprod ... 007/cat/31This doesn't answer your question, but I hope it helps.