Here's the story... Lately I've been getting a lot of requests for CIFS services on my filer. Until recently I have been able to avoid a lot of windows interaction but that time is coming close to an end.
My Observations:
Adding Cifs to your mix shouldn't kill CPU unless you are heavily using crypto or smb signing.
Performance is typically greater than both Samba and Windows for bread and butter file server operations using CIFS.
YMMV, but if you aren't seeing significant CPU usage or I/Os now, adding the additional Cifs clients shouldn't cause you any grief.