I'm not sure where one can find stats about "general" users, but
stats on 22K nodes do show a spread of versions.
Try
Bitnodes.io Maybe it could be of help..
though depends on your set prune size.
So far you have the required backup space then you can always archive it.. you can also test it by running it directly from the external drive before you start the upgrade as the copied file could be corrupte sometimes, you can do that by changing the
-datadir path to the new exter drive path , if it works then you can revert it and go on with your upgrade... make sure you revert it though.