Are contents of ConfigAndLog directory safe to delete?
The main use of those logs files is to help diagnose problems in CiviCRM.  You're unlikely to want to review problems from a few years ago so you can delete them.  The one without the datestamp is the current one and that should have the most recent timestamp. 

However 9GB is a lot of log output!  It would be worth looking at the recent ones to see if there are current issues that need attention.