Rent Me a Dress

Have you ever heard of Rent the Runway?  Ever used it?
The idea behind the site has intrigued me for awhile.  Basically, you pay a rental fee to get a designer dress for a few days.  I've always thought it was a really good idea, especially because I tend to buy dresses, wear them once, and then feel compelled to buy another one when I have the next special occasion.  But I have never bitten the bullet and tried out the site, opting for dresses from non-designer labels that are available locally.
Well, my cousin is getting married next month, and I need a dress.  And this time Rent the Runway is even more tempting because I really don't want to buy a dress in the size I am now because (fingers crossed) I will not be this size for very much longer.  I have looked at the site over and over, and am really excited by some of the options, but I still am a bit wary.

Choice 1

Choice 2

Choice 3

Choice 4

Choice 5

Choice 6

I should probably mention that the wedding is an early evening, outdoor affair.  It's on a plantation with a relatively casual feel if that makes a difference.  

Also, Rent the Runway has a pretty awesome policy in which you can rent additional dresses for just $25 each, so I'm kind of thinking I might just rent two.  This way if one doesn't fit I have a backup, and if they both do fit, I'll have one for the rehearsal dinner as well.  

The only risk, then, is if neither of them fit, I am pretty much screwed just days before the wedding, since they won't arrive until the day we have to leave to get there!
So, I need you all's help.  Tell me what you think...do it or not?  And then which of these fine choices do you like the most?  Please, please, please comment and tell me what you think....even if you don't usually comment...I really need all the help I can get on this one!