I noticed that Ext.each is used very frequently. It's a very convenient and flexible way to iterate, but it is also slow.
I suggest adding this mapping and using Ext.forEach instead of Ext.each.
forEach is faster because it maps (in newer browsers) to native forEach. I checked the Ext code base... in many (if not almost all) places each could be replaced by faster forEach because we don't check the return value of the callback.Code:Ext.forEach = ExtArray.forEach
This shortcut would also save a few bytes because it could replace Ext.Array.forEach in a number of places