Thanks for testing these out.
I'm seeing a noticeable boost in speed for the listed hashes, but it wasn't clear whether $crc and $md5 were already considered to be optimized, or just not a priority.
$md5() was already using the larger buffer. $crc() is actually a much older implementation located elsewhere in the source code which I didn't look at. I have increased its buffer size as well in the next beta.