The overall performance impact of 4.1 is not as good as I hoped for.
Here's an example from an app of ours. Doubleclicking a grid row opens a new Ext.window.Window with a four-tab tabpanel with a few grids:
With ExtJS 4.02b that takes about 1760 ms:
ExtJS 4.0.7 brings it down to about 1060 ms:
With ExtJS 4.1 it's still about 863 ms:
In all cases the provided ext-all.js was used. The values varied by about 50 ms per individual test.