I ended up knitting two swatches. I started on US 4's and thought it was too tight, so I ripped and started again on US 5's. Once I'd blocked that swatch, I thought it was too loose, so I went back to the 4's. I felt a little bit like Goldilocks :-)
By the way, here's a little trick I use to keep track of the needle size. I put eyelets and purl bumps in the lower right corner (knit an eyelet as a yarn over followed by a knit two together).
Once both swatches dried, I hung them overnight (this is what I referred to in my last post as "weighting").
And today, I took my final measurements.
Yep, the US 4 wins.