My wrist is 17.5c. I had the 40mm for a few days but it was uncomfortable. I was in between holes on the sports band and even with the link bracelet I was in between links. I also tried it with the Milanese loop but the same problem. The 40mm had too much room to move on my wrist. As I like to have the watch loose enough that I can bu my index finger in between the strap and my wrist. What was happening was the watch was twisting over to the wrist bone and resting there.
Returned it and got the 44mm and it fits perfectly.