The number of slides is irrelevant. Slides are just a tool to help you
enhance your presentation and should be thought of as such. After you have
outlined your presentation and detailed out your speech points, then decide
how to design your slides that would poise the most value to your audience.
In my experience in working with speech presentations with clients, every
client is a little different. Some speak to script, some use notes, some
wing it- some embellish on stage, some race through it and forget half of
it-- and a successful overall effect with the audience will take into
consideration the speech, the speaker and the slides as well as the
environment (room/projector conditions). CUSTOMIZE YOUR SPEECH TO YOUR STYLE
and NAIL YOUR TOPIC -- worry about the time and the number of slides last--
(if you go short and its good, no one will care!) ** Good Luck!!! **