Performance after upgrade was good if not better. I just upgraded because I wanted a root and thought oh well, why not get ICS too. At the time of upgrading, my phone did not show an OTA update to ICS. But yes, ICS has been officially out for LWW for a long time now. I personally did not like ICS, preferred GB.
After I flashed it with ICS, my phone then showed an official update to another higher version of ICS. I did not flash it OTA as I was afraid I was going to loose root.