My best friend is getting married next weekend, and I'm her bridesmaid! She's been extremely low-key about the wedding. No coordinated outfits and I'm her only attendant I believe.

It's time to decide for sure what I'm wearing, and I can't make up my mind. It's a late afternoon ceremony (5:30pm). She and her guy will be in traditional wedding garb (white dress, tux). The wedding and reception are described as "Dress to impress! Or simply to be comfortable" which means she's hoping everyone will enjoy the chance to dress up, but with no particular dress code. Most of our friends' weddings have been similar so I know what this will probably look like.

The dresses I'm considering are fairly casual. The first is perfect for outdoor afternoon weddings - in fact, I wore it as an attendant in my other best friend's wedding last summer. It's an Eileen Fisher linen slip dress, silvery grey with subtle metallic threads.
http://www.pinterest.com/pin/514536326148163528/

Another option is to buy a new dress. This AllSaints white silk shirtdress with an inkblot-eseque print caught my eye:
http://www.us.allsaints.com/wo.....ategory=22
On me, it is knee-length, so the length is entirely appropriate. A shirtdress is more casual than I'd choose for many weddings, but I think for this one it's an option.

I have another dress (also white silk with black inkblots... I detect a theme) which I love, but it shows a bit more skin than seems ideal. I have no good photos, but here are two bad ones:
https://scontent-b-sjc.xx.fbcd.....7676236640
https://fbcdn-sphotos-g-a.akam.....8965816516

I've asked the bride what type of look she'd prefer, but I'm curious what you all would choose. (I do have a few other fancy dresses, too, and I can justify the cost of a new dress if that's the right choice.)