I know how daunting looking for a wedding dress can be. I've been engaged for 4 years and have not gone shopping for a dress once, ahh... I have issues with that.
I think the infinity dress is much better than the prom dress. The only issue I see is that it might be so difficult to find a bra choice for it. I think that once you resolve that issue, the dress will fit much better. Maybe that is what is giving you the uneasy feeling about it.
Also, since the fabric is not stretchy, I would be so afraid to expose myself accidentally. That fabric might "dislodge" itself during the day. Jeje, we all want a memorable day, but not in that sense...
I don't know. I think the infinity dress has definite potential, IF you can resolve the bra situation and you are 100% sure the fabric does not move around. I will sit, lift my arms etc. to make sure the fabric does not move.
My favorite is the grecian look on #8.
If you decide to shop for a dress, check Ann Taylor and J crew, they have lovely evening frocks and bridesmaid dresses that will fit the bill for what you are looking for, and are not as pricy as a wedding dress. Actually, you can look at bridesmaid dresses in general ( in white, ivory etc) as well.
You will look gorgeous even with a potato sack on, so no worries:)