Ok, your metrics are correct, but not useful.

There's little point measuring both things together:

Code:
var start1 = new Date();
Ext.Ajax.request({
    success: function(){
        var start2 = new Date();
        console.log('Ajax time', start2 - start1);
        // do rendering
        console.log(new Date() - start);
    }
});
If a majority of the time is spent doing the Ajax request, the problem is on your server side, so it's well outside the scope of this forum.