Okay, then. Not a single vote for smaller, so I'm sticking with this. Although Bijou, yes: a size 5 would probably be just perfect!
Interesting things to ponder about sizing. Thanks everyone for chiming in.
Notsaf, I agree this really connects back to my/our preppy New England roots. I actually remember quite vividly convincing my mother (at about age 10) to buy me a navy blazer from the boys' department!!! When something is ingrained that deeply it's hard to let go of.
Lisap, ego is also likely a part of it. Going up a size can be hard, although I have come to peace with some of that. But in a situation like this, where I feel like I can justify the smaller size, it can be a minefield. I like thinking about the elegance of a looser fit.
And Roxanna, great point about the fabrication. I think you're right on that linen in particular needs to have some ease.
Helena, you should try barre! I've been doing it for years now and it's a great workout for muscle toning, strength, and flexibility. Some small weight-bearing for arms/shoulders/back and a lot of body-weight bearing (planks, pushups).