Don't make the mistake of thinking that having every word in front of you means you can practice less. As an actress, I gave many performances without scripts, but I also performed in several productions from visible scripts—where we stood in front of lecterns and read our parts. We spent just as much time in rehearsal with productions when we read from scripts as we did with traditional productions when we memorized. It is just as hard to read and be outstanding as it is to memorize and shine.
If you are extraordinarily fortunate and have a speech writer who knows your style and is a good writer, you can get by with one or two practices. But that person is rare, and a talented speech writer is usually expensive too. In most cases, you will have to tinker with the words yourself.