I found that different fonts require different values for Optical Metrics. On my old hardware it takes 15-20 minutes to run. It would be good to have a quick preview so that one can test which value is likely to be best for a particular typeface. After that quick preview, its not difficult to undo and try again with a new value if its not quite right when tested on a full character set.
Here are some tests with values ranging from 16 to 27 for different typefaces. The screen shots were all taken with Kerning enabled.
