Need benchmarking advice

Our organization is getting ready to install a 30-day trial of Diskeeper Professional software. The actual purchase will be quite costly so I’d like to do some before and after benchmarking on the 7 servers and several workstations that will run the trial software to help determine if the improvements warrant the purchase. We are a non-profit so I’d need to use some freeware or very inexpensive tools for this. One server runs SQL and and Exchange Server. Any suggestions on what software and what tests I should run? Thanks.