Hello,
For my test I have used the basic example in ext-4.1.1a\examples\grid\array-grid.js I have just modified this lines (comment the renderTo in grid and add the grid.Render() + time execution calculation) :
Code:
...
var grid = Ext.create('Ext.grid.Panel', {
   ...
   //renderTo: 'grid-example',
   ...
});
var start = new Date().getTime();
grid.render('grid-example');
var stop = new Date().getTime();
var executionTime = stop - start;
console.log(executionTime);
The result are :
IE9 : ~3000ms
IE8 : ~150ms
FF v16.0.2: ~80ms
Chrome v23: ~60ms

I don't have a support licence, in can't test if 4.1.2 or 4.1.3 solved this performance issue that are unacceptable for my client who use IE9, and I can't force them to use FF or Chrome.