Togheter EPiServer CMS 5, DropIT Extension X3, the EPiCode EPiServer Web Parts and your custom integration code makes a great team; The Fab 4!
By combining those three (and not "tree" as one reader correctly pointed out :-)) you get everything the editor AND the web site user will need to create great sites including the ability to make per user customization.
To be able to combine the web parts framework and X3 on the same page you have to recompile the EPiCode Web Parts framework after you have made the following minor adjustment: Let the TemplatePageWebPartbase inherit from the ExtensionbaseTemplate (in the Extensions core library). The a web part page will be able to host both web parts and Extension function.
When and why you ant to combine them? I'll soon create a table with the possible combinations and reasons you would do it (some pros and cons) ... if time permits it ... :-)