Suppose it depends rather entirely on what the customer is expecting from their new AP.
Coverage, Speed, Ease of Configuration, Price -- you'd want to plan your demo to play up the parts where Aruba IS better than the others, and argue for why the overall combinaion is best from Aruba.
If you're doing a throughput test, or speed test you'll want to make absolutely sure the back-side switching/routing is beyond the specs of the iAP. Also make sure the demo client is up to the full specs of the iAP - otherwise you'll be demoing the client and switch and the iAP won't be able to shine.
I know I haven't really answered your question, but without knowing what you need to show this is the best I can come up with.