I just ran a Lightworks rendering speed test using the same file, once while booted from a system folder containing QT 4.1.1, and again while booted from one with QT 5. The only difference between these folders (afaik) is the QT version. They are on different partitions of the same hard drive. I ran the test twice and 5 is almost 3 times faster! Has anybody else seen this?
Be aware that the update may delete the Lightworks Raymaker extension, so save a copy outside of the system folder. It deleted mine and that's how this whole thing started....trying to figure out why renderworks wasn't working.