I've noted that you use Array.slice method in Ext.AbstractContainer.add method:
add : function() {
        var me = this,
            args = Ext.Array.slice(arguments),
            index = (typeof args[0] == 'number') ? args.shift() : -1,
            layout = me.getLayout(),
            addingArray, items, i, length, item, pos, ret;
But as far as I know this is not the fastest way to copy all values from arguments objects:
So I'm wondering whether Array.prototype.slice usage is appropriate in such a common used method.