At the risk of redirecting your question, aren't we forgetting the most important part of this equation? Your Net! I'm an owner as well, and what is important to me is the value I'm getting. We all know there are some brokers that will work extremely cheaply...usually delivering extremely cheap results. A good broker shows you rent comparables to help you confirm that the lease rate you're getting represents at least market. If you're getting a premium over market, then why not pay a touch more commission--particularly if this is a repeat business situation where you want the broker very motivated to bring you more tenants.
If you could have gotten the same rent yourself, then it's not really worth paying commission. Is your broker adding value to the entire process? Helping you manage risks and liabilities? Making sure you start off on the right foot with this tenant? My guess is that if the broker were performing in all of these essential areas, you would not have posted this question. At a minimum, interview 3 more leasing agents for perspective.