Atlas gearbox sprocket size

The sprocket on my Atlas is 19 tooth, which I think is standard. It is a late 67 model year, pretty original bike. I was wondering what other folks run on their bikes? I like tall gearing, my Commando has a 22 tooth sprocket. Has anyone ran a 20 or 21 on their bike? While it is apart, I was thinking of going up a bit.