lammert - 9:53 am on Jan 18, 2012 (gmt 0)
Hi rosglo, first of all Welcome to WebmasterWorld!
If you wan't to test the real-life performance of the server including the performance of the storage subsystem you may need to test it with the real media files you have there. Is the server already filled with all the downloadable files? Otherwise the test results may not be realistic.
The ab testing tool which is shipped with Apache does a real GET request as far as I know. The only problem is that you specify the name of the file to get on the command line which makes it impossible to specify a list of random downloadable files to properly test the random file lists.