The methodology should be to pave the way to living in the Cloud — even if you still operate Outlook on the desktop. Gmail is a Cloud application.
This configuration takes a bit to set up and takes maintenance! If for instance you change passwords at ICloud?
The point being that if each node is being sync’d to the others — a change made in Gmail will eventually replicate to Outlook Contacts. Other configurations are possible — but have lead to dupes.
Love to hear from others how they’ve accomplished a cleaner means.