I havent timed anything but it flys through the thumbnail generation AND (atleast on Windows) uses less CPU Usage.. The normal version would create 2 php-cgi.exe processes and would take 50% CPU usage a piece.. this one still creates 2 processes.. but only used about 12-22% each and doesnt run for as long...
Not sure that there should be a difference in image generation speed -- it uses the same i.php, but optimizes gallery display and filesystem/database access. Still should be much better though.