I have observed that BetterZip is a fraction of the speed on the commandline unrar when extracting large files (DVD ISO multivolume). I have not tried to compare small files as its too fast to easily notice. What takes unrar 2-3 minutes to extract takes at least 10 minutes with BetterZip. This is on an original 2GHz dual G5 with 4GB RAM running 10.5.5. If the decompression routines are straight from the open library, then perhaps the difference lies somewhere in file I/O routines (different read/write sizes, buffer size, etc).