But wait – there’s more. You could place banners at the bottom of your HTML page (after all content) and then use javascript to reposition the banners. What this does is give the rest of the content higher priority and it will have a better chance of being loaded first.
To help with this, please see this worked example for End of Page delivery: eop-example.
Inside the zip file is an HTML page with 2 spots for banners, as well as some fascinating content. At the bottom of the page are 2 invocation tags as well as a call to a javascript function which will reposition the 2 banners to appear above where they are meant to. The javascript file can most likely be kept as-is.
What other things can you do to help speed?
Caching is important. OpenX has built-in caching which limits calls to the database – in a production environment you might want to increase the cache time used by your installation. You might also want to install a caching system for PHP on your server.
Keep in mind what 3rd parties you are using for banners. If you are using external image banners or 3rd party HTML banners, not only must OpenX deliver the banner but the 3rd party must then deliver the image/HTML. Sometimes such external sources can be slow to load and should be kept in mind when analyzing speed.