I'm convinced that mysql is faster as normally you are writing and deleting to a file instead of to a database (which is almost ALWAYS memory based). Do you have any idea how to set it up, though? For me adding the parameters like "container_cfg_mysql_username" (like demo 55) just cause an error....
The chat log seems to be still kept in a file. Not sure when it is updated though or where that is in the code. (If it was kept in the db the chat performance would be even faster.)
so, to the best of my knowledge, mysql (a db) is better off than file based system. and yes, you can turn of the file logging and just log to db, by directly modifying the file container class. hope it helps