On the other hand you can use the GUP monitor tool or enable loggin on the apache side, it will show you the kBs transfered to the clients
https://www-secure.symantec.com/connect/forums/sepm-12-apache-logging-show-content-size-sent-clients
Symantec Endpoint Protection (SEP) Content Distribution Monitor / Group Update Provider (GUP) monitoring tool
http://www.symantec.com/business/support/index?page=content&id=TECH156558
That appliles to SEPM also, as it changes everyday you cant say exactly what I have seen is 550 to 600 MB