Thanks for doing these tests. I have also done some testing myself with piped files from disk using a buffer size of 8k. For my tests there was no noticable difference in speed, so I will lower the $CHUNK_SIZE to 8k for the next release. This should provide you with most of the speed benefits you get using 4k blocks. I felt a little uneasy going less than 8k due to the potential of increasing i/o overhead on systems with slow CPUs, so 8k sounded like a good compromise.