For some time I have suspected that the file name display and progress bars slow down file operations slightly. In particular, delete operations are noticeably affected.
To test the theory, I did some experiments. I set up a HDD with lots of files to delete (over 50,000 with long random names) and made an image of it. I then repeatedly restored the image and tried different methods of deleting the files.
Turning off Cleartype speeds up deletion by about 15%. Turning off themes makes a 3% difference. Moving the progress bar window so that it is off screen (and thus not being drawn in XP, Vista does still render it) makes a 24% difference.
Conclusion: Rendering every file name and the progress indicator slows down certain file operations, particularly deleting. Opus could be ~25% faster just by only updating the display only say 10 times per second or less.