Split test your wordpress theme, and track test using Google Analytics user defined values.
Simple - go to http://www.yoursite.com/?wp_splittest_reset
No - this lets you split test whole themes rather than content changes, e.g. navigation on the let versus navigation on the right
Check the source of your webpage for a line that looks like this:
Make sure all of your themes call wp_footer() in the footer
Yes, it works with either old-style (pageTracker) or new-style (_gaq) analytics code