I want max compression on my ssh tunnel cos I’m on a dialup line 
At the man page can one can read:
CompressionLevel
…..The meaning of the values is the same as in gzip(1). Note that this
option applies to protocol version 1 only.
What if I want max compression rate and while using ssh version 2?
How know the protocol version I’m using?
To know the protocol version of ssh, you can include -v option in your ssh command.
To request compression, you can use -C option. This should work even for protocol version 2.
Check more discussion of this question.