FWIW I updated to firmware 4.03.01 and experienced no issue after the update. It was tempting to immediately hit the home button after the update to see if anything changed, but I left it alone, continue to watch what I was watching for about 45 min, then hit the home button. There was no issue with slowness what so ever... Didn't have to go through the initiation of premium either. I think this firmware update somehow requires all the apps to be re-downloaded and installed so I give it the time to do what it needs to do.
Just sharing since so many here experienced issues.