This is one of the most interesting questions I've seen recently !
The short answer -
As far as I can tell compression and decompression is part of the kahuna domain - it isn't CIFs specific.
You might want to try and look for a correlation between CPU(or kahuna) and cifs read activity in OnComand Unified Manager (DFM).
I don't advise customers to turn on compression in high read activity environs, we do caution that it can be a CPU hit on decompression.
I'm going to try and run some tests on my lab environ here, and see if I can tell you any more...
I hope this response has been helpful to you.
At your service,
Eugene E. Kashpureff
Senior Netapp Instructor, Unitek Education
(P.S. I appreciate points for helpful or correct answers.)
Me thinks I'm in love with my job !