If cost/benefit is a concern, I suggest buying complete. It'll be more expensive to buy all quality components separate, but if you plan on buying complete and upgrading every part anyways, it might be worth looking into.
The biggest difference between the Flite100 and the Lightening is the frame. The Wabi fully built will be lighter because of the scandium aluminum tubing, as opposed to the Reynolds 520 found on the KHS. Other than that, you'll have to look closer at the geometry to get a general understanding how the thing rides. I can't speak from experience about either bike, but my roommate has a Flite100 and he seems to like it good enough.
http://www.wabicycles.com/lightning_frame_detail.html
http://www.khsbicycles.com/Images/Ge...-flite-100.jpg