benchmarking rsync's -z compression utility

[Leaw, Chern Jian]

Hi,
Is there a way in which rsync's -z compression (zlib) utility can be
benchmarked? 

I'm trying to compare the compression ratio between rsync and external
compression tools like gzip and bzip2. 

Are there any advantages to using rsync's internal compression mechanism
specified with the -z option compared to solely applying external
compression i.e. bzip2 to the files and invoking rsync to transfer these
files without the -z option?

Thanks