Cache calculation time and storage estimation can be estimated by caching a small extent before starting to role out the whole cache. See chapter Storage and Time Estimation for caching for details.
To improve the cache performance it is recommended to always increase the number of instances of the map services to be cached. For information on how to setup map service properties see chapter ArcGIS Server Map Service for details.
Another performance issue to be taken into consideration is to never calculate a cache from data stored in a versioned database. Performance losses will be enormous.