For my version, I've chosen Grignasco Champagne (75% extra fine merino, 25% mulberry silk; 165 meters/50 grams) in a soft periwinkle color (#375) knitted on size US 5 (3.75 mm) needles. Because I'll knit the sweater in rounds, I worked my gauge swatch like a giant I-cord, knitting across the stitches, then sliding them back to the needle tip, bringing the yarn loosely around the back, and knitting the stitches again. In this way, every stitch is knitted on every row, just as when knitting in rounds.
The back of the swatch is a bit of a mess:
But the front shows smooth stockinette in which every row is knitted:
My gauge on the unwashed swatch is 29 stitches and 38 rows = 4". (The 5 purl stitches near the bottom are there to remind me that I knitted this swatch on size 5 needles.)
After washing and blocking, my gauge changed to 26 stitches and 38 rows = 4". Don't ask me how the stitch gauge can vary while the row gauge stays the same.
Because this yarn contains silk, there's a good chance that it will stretch with wear. Therefore, I'm hanging the swatch and weighting the bottom with binder clips to simulate what might happen after the full-size sweater has been worn a while:
I'll measure the stitch and row gauge tomorrow to see if there is what's called a "hang gauge" that might affect the finished size of the sweater.