Willy,
Have you tested rsyslog? I've had bad experiences with syslog-ng dropping messages in the past, though the logging configuration was fairly complex.For high loads, I strongly recommend syslog-ng. It's the only one I found which managed to log more than 10000 logs/s without dropping any :http://www.balabit.com/network-security/syslog-ng
It was at least able to report how many messages had been dropped. This was with an older version of syslog-ng as well.
-JohnF
