With all due respect, 20Mbps is not really a great deal of capacity for a mirror. One user could use that amount, when either completing an initial sync or downloading large files. It might be worthwhile possibly increasing the capacity of the connectivity to your server.
In saying that, I feel that I can speak on behalf of the CentOS Project in saying that everyone appreciates your contributions regardless, as every server counts.
Regards,
Christopher Hawker
*Note: I am not a representative of the CentOS Project, or any of it's related entites.