Thanks for the feedback, ladies. I definitely agree that not all sizes are made equal and can vary based on manufacturer/designer. I just tend to stay in styles/designers that work well with my body type regardless of size. For example, my proportions definitely don't work with Ann Taylor stuff, but almost always work with INC, much of Banana Republic and Donna Rico. I'm sure if you go true designer (Prada, Chanel, etc.), then the sizes change even more as I know that they run larger (if you're going to spend $500+ on something and you're usually a size 8, but a size 6 in that dress, it will make you more likely buy it).
It's just so interesting to see the body compositions and how they change. At 168, I was a comfortable 8 the vast majority of the time (sometimes 10), so I imagine at 160, it would have been loose on me and I have even been wearing some size 6s, but you ringmaster, didn't reach a comfortable 10 until 160ish (for me that was closer to 180).
So I'm hoping more 5'9" girls will ring in and we can see an interesting range of weight for sizes 6 and/or 8.