Export archives to their original mailbox size difference

Hello,

I'm doiing a capacity planning for our organization and I would like to get a vault users utlization report like If I use the  Export archives to their original mailbox method and unzip the archiced mails to the original mailbox what would be size difference.

Please help me to get the report on this.

Our vault version is 8 and 9 and a cluster environment

Regards,

Mikey