Alfonso,
In our Effeciency Dashboard, the only other options we have besides Global are groups which are comprised of physical systems.  So I have a group called FAS3170 which contains the two nodes for that filer.  That shows in my drop down list for the Effeciency Dashboard.  I have other groups created, e.g., Vmware-NFS which work fine within the Operations Manager, but are not listed within the Effeciency Dashboard.
Perhaps the Effeciency Dashboard only works with groups comprised of physical systems/hosts.
Thanks!
Jason