Should you decide that Mean Machines are not for you, there's always
Mumble Clan. We're relatively small and of 4 1800+ elo players only 2 are active, at most, but that might change anytime.
I'm not sure how cooperative we are. My goal when creating the clan was to advertise the mumble server and to offer interested players cooperation far beyond the current average, but there's no rule yet as to how competitive and organized members have to be.
That said, I really suggest Mean Machine gives voice communication a serious try. When done right it's much more efficient than markers and chat, simply because voice chat does not clutter the UI and allows team members to provide information without taking away apm (eg to type, to zoom to a location, or click on markers). Don't be afraid of bad pronunciation, if people don't understand you they'll let you know. You can always stop.