Exchange powershell script to find all users mailbox sizes

Hi guys, I'm using the following script to tell me how big everyone's mailboxes are.

Get-MailboxStatistics -Server 'SERVERNAME' | where {$_.ObjectClass -eq “Mailbox”} | Sort-Object TotalItemSize -Descending | ft @{label=”User”;expression={$_.DisplayName}},@{label=”Total Size (MB)”;expression={$_.TotalItemSize.Value.ToMB()}}  -auto >> “c:\Temp\mailbox_size.txt”

Pretty straight forward, exports as a text file.

I want to archive the files for future reference., so how can I have the text file created with the date & time it was created in the file name?

thanks in advance :)

Shane