I did the math, after checking with rlseiver to confirm that it needed an inverse proportion. It looks like I am more likely to need size 8 anyway. I do have 2 size 8 circs, that had been working on the braids cardigan, but since that's on hold until I order the bigger buttons, I can use them. One of them is VERY long and would be a pain to use for the whole thing - but I can use it to swatch with. So I've cast on a swatch and started it.

And then put it aside, because my shoulders hurt and I feel down.