log4j 2.x async seems to outperform log4j and logback according to their tests at https://logging.apache.org/log4j/2.x/manual/async.html#Performance
It would be nice to make use of it at some point.
Migration to log4j 2.x seems equally easy as logback since both have sl4j bindings, https://logging.apache.org/log4j/2.0/log4j-slf4j-impl/index.html