megan,
I was thinking a bit more. It would be reasonable, if you got good shots in good conditions, to expect 10Nms as a good ballpark figure. And even in a little turbulence 20Nms should always be possible with a bubble periscopic sextant from a jet transport. My last nav sector using stars was in May 1975.
Perhaps, there are others who can add to this. But I know next to nothing about pre-war astro navigation.