Your heaviest load times are going to be either the JavaScript itself or CSS files in the head section. This is due to the fact that when JavaScript or CSS is being parsed by a browser it typically just uses one connection to do so where as other elements in the body section load through multiple connections. In short all attention is focused on parsing the JavaScript and the other elements have to wait until the JavaScript is parsed to render.

That is why doing this sort of thing in Web pages is notoriously poor:

<script src="blah1.js" type="text/javascript">
</script>
<script src="blah2.js" type="text/javascript">
</script>
<script src="blah3.js" type="text/javascript">
</script>