Well, I just glazed again over my my.cnf for our web-cluster because I just moved a database from one cluster to another and getting quite different performance from it. So, as I expected, there is a slight difference between both configuration files:

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@@ -55,8 +58,6 @@
 innodb_log_group_home_dir       = /var/lib/mysql/db
 innodb_log_file_size            = 512M
 innodb_thread_concurrency       = 8
-sync_binlog                     = 1

And apparently, according to the MySQL Performance Blog that’s really, really bad (as well, we’re currently running without write caching, as the battery module of the storage is dead).