Choice of "rich" Javascript framework - jQuery and ExtJS

After the recent work with the excellent JQuery table
widget, I've had some discussion with Bob about the advantages of
using one framework for GUI.

We are already using JQuery a bit, and MapFish and GeoExt for the GIS
part. Both JQuery and Extjs are excellent frameworks.

Here is a well-reasoned recent discussion of the merits of each:

I think it could make sense for us to gradually transition to Extjs -
it has an excellent selection of components that work with JSON and
can be cobbled together with listeners etc.

Here is a stab at an orgunit tree with 6800 nodes (fetched
asynchronously from the db):