Might want to take a look at the free construction guide for the Wally Wing made from a $4 Walmart hand chuck foam glider. Not much harder than a Zagi to build, flies a little slower, soars a little better yet still does stunts (videos at site)
http://www.acesim.com/rc/wallywing.html
For a stunt wing that will fly circles around a Zagi, check out the Super Cutless version of the JSF. Made from foamboard, it can be flown with an IPS up to a geared S300 for vertical performance plus quick disassembles flat for transport.
http://www.acesim.com/rc/jsf/jsf.html
(bottom of page)