Our service offers one of the fastest backups that is available.  The way we do that is by running a special service on our servers that works with our backup software.  The service does the MD5 check sums very quickly as well as the file and directory listing.  This service has been tested very thoroughly.  Just by using this service has proven in some customers to decrease the time of the backup by 45%.  The larger the backup set, the more time you will save.