What irony...Ed is the very one who spoke about the Extjs v4 performance *improvements* over v3 in the video presentation, when (once the class system changes were put in) v4 became much slower than v3. This performance problem was never fixed, and many of us had to stick with v3 because of it.
So ... Ed left Sencha, joined C3 and migrated them away from a "Sencha framework" in order to achieve an"enormous performace improvment".
From Ed Spencer's linked in:
Lead UI Developer
C3 Energy Network
June 2012 – Present (2 years 5 months)Redwood City, California
My chief contribution to C3 has been the architecting and development of the UI framework that now powers all of our products. Built on the solid foundation of jQuery, Bootstrap, LESS and a handful of other open source technologies, it has delivered an enormous performance improvement over the previous tech we used (which happened to be a Sencha framework), as well as a similar improvement in our development productivity.