One year ago I have switched from PureFTPd to ProFTPD because it runs smoother on the virtual server I am running. The server is really easy to setup and maintain, but with the standard configuration it always takes around 5 to 10 seconds to log on to the server. After searching for a solution to these slow logins, it turns out that there is even a point in the FAQ on how to speed up the login process.
Just edit the file
/etc/proftpd/proftpd.conf and add these 2 lines:
Lesson learned: I should read manuals more often.