Your score on the essay section of the GRE exam is used by graduate schools to evaluate your writing and analytical skills. Two separate trained readers will read your essays. They will score each essay based on many factors, and the scores will be combined and averaged. Scores are given on a range from zero to six, in half-point increments. The ETS provides the criteria that are used to score the issue and argument essays. Although in the essay section grammar and spelling are important, it is much more important that you concentrate on writing a coherent, complete, and persuasive essay.
Your article is well written, but seems rather incomplete in its examination and I would like to point out just a few concepts: I quote you "The whole objective of most speeches is to convey information, or to promote or defend a point of view" and "The essence of a good speech is what it says". The above is only part of the story, other objectives also include inspiring an audience and persuading them to align with the speakers point of view. These objectives are of primary importance. The true value of a speech is measured by how closely its effect on its audience matches its intended purpose. Even brilliantly written speeches that are poorly delivered can never be moving, meaningful or memorable to their audiences. Yet there are speakers that ramble and who are less than eloquent in their chosen words that are capable of moving great masses of people. I don't know how to measure the relative importance of words, voice tone and body language within a speech. I would suggest that it depends on the audience, the situation and the intent of the speaker. However, I would also suggest that the way in which words are used in a speech is of less relative importance than in written language, and possibly even secondary in some cases. Wikipedia has an interesting article on the subject of "Rhetoric" for further reading.