This app will quickly split up a large WoWCombatLog.txt into separate files for each fight attempt, named after the time and encounter name (example: 2018-04-15T13.17.07_Argus the Unmaker.txt)
On an i7-6700 PC with an SSD, it was able to split a 4 GB WoWCombatLog.txt up into 408 distinct encounter attempts over the course of 5 minutes