Is the 85L incredible? Yes, and it is what I would recommend, hands down. We use it for every portrait event, BUT not every wedding, it is just... too... slow...
That being said; I did use it for the bride walking down as well as various dancing shots at a wedding we had this July. http://photosbytabor.smugmug.com/Tulsa-Wedding-Photography/Lisa-Isaiah/i-R6GPLb2/A
Since I had displaced a rib just a few days before, I updated their wedding to a 3 photographer event, (myself essentially being the third photographer). I figured, what the heck, I'll see how the 85L will handle action. I was wonderfully surprised actually. One of the many things that helped me during their wedding was a great deal of ambient light, wonderful shadows, and I would prefocus my shots just before I would focus/shoot, (basically I would focus quickly, twice, and then fire). This helped save my keep rate, but it is not something I would recommend everyone try, especially at a wedding.
For stills/portraits, it's incredible in essentially every aspect. For weddings, there are so many better options, most notably the 70-200 f/2.8L ii. Though not as wide, amazing, amazing, wedding lens. We used all of our lenses during that wedding, (apart from the 17-40 so look around the gallery (or galleries if you keep going), and use the info button in the bottom right to see if the shots you like were taken with the 85L.
As always, you could rent the thing, but yes it is well worth the money, just maybe not as a dependable, moving target at a wedding, lens.