he does not care about technical performance because he does not understand it - unless he is from an IT etch background, in which case he would already be agreeing with you. You need to simplify your arguement and put dollars on it.
Prepare a report for him and then deliver it with a short summary, written and verbal. Detail the security issues and the costs of securing the wireless network properly; include the performance and technical stuff and an appendix, not in the main document.
Set out why wireless is so easily intercepted and thus needs all traffic to be encrypted unless he is happy to have everyone in the world being able to read his traffic. Then cost out the software and maintenance of providing the encryption with the cost and maintenance of the wireless network. Then do a report on the cost of installation and maintenance of the wired network. Let him look at the bottom line cost for both systems with 5 years of maintenance involved - make sure to include staff costs.
With the security side include some printouts of industry articles on wifi security problems. If he is not convinced the security is required and the costs are cheaper you will never win the point.
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