I can answer your questions in part. Goldenrod and the Asters are the last plant to give nectar in my area of Wisconsin. After that there is nothing. Someone told me that it is variable - sometimes the Goldenrod will give up to 60 pounds a hive, and sometimes very little. Additionally there are several types of Goldenrod and they don't yield equally.
I have only been keeping bees since 2008. For a more precise answer I bow to the generous and wise Wisconsin Commercials beeks: Sheri, Roland, and Shannon are you out there?

Adrian.