Twisted has a benchmark suite and release-to-release tracking of performance information, so that we can be sure optimizations have a positive impact. http://speed.twistedmatrix.com/timeline/
This link is flawed. It points towards eventlet but gevent is significantly better. Not sure why Ted felt otherwise, but I speculate that it's because at the time of writing gevent was considered incomplete compared to eventlet.
To be clear: gevent is significantly faster than eventlet and offers the same functionality.
Twisted's event loop is faster than gevent and tornado. http://cyclone.io/
This test is for a pointlessly weak concurrency level of 25. Under serious load the difference is much more gigantic showing that Twisted can't handle the same load as gevent.