maximum block-size (-B) parameter

[Rob Bosch]

I've been trying to test rsync on files over 80GB again to see if I can find
ways to improve performance further.  I tried passing a manual block-size
value and I keep getting "Invalid block length" from the [sender].  Can
someone refresh my memory of the valid values that can be passed using this
parameter?  

I've tried passing 1048 and the -vvv output shows the file being processed
in 1KB intervals.  I pass 1048576 and I get the error message from the
sender.  I have not modified the define in rsync.h, it is still ((int32)1 <<
17).  Since the value is an int32, passing 16MB or 1MB or 512KB should not
be a problem, right?

Rob