Question

Is the structure below correct or is the section tag not needed?

For SEO, assuming the relevant keywords are the page title not the site title, is the structure bellow the best optomisation? Thanks

    <header>
        <h1>Site Title</h1>
    </header>

    <section>
        <h1>Page Title</h1>
        <p>Page Content Here</p>
    </section> 

Answer 1

Don’t abuse the usage of section and article tags using them for structure, instead keep using divs.

In html5, when using headings and sections, you must check that each section has its own title. You can use the outliner to see how is the structure.
http://gsnedders.html5.org/outliner/

According to your case you’ll notice that the Site Title has still more relevancy than the Page Title. That’s okay. But better use a div for dividing the header from the content.

// Reply 12/03/01

You can try using some weird position absolute to achieve your goal:
First of all, the section must have a heading, if not it will be null.

<header>
   <h1 id="position-me-in-section">Page Title h1</h1>
</header>

<div id="content">
    <section>
        <h6 id="position-me-in-header">Site Title h6</h6>
        <p>Page Content Here</p>
    </section> 
</div>