DAM or Document Mgt SW for Mac's in a Adobe CC workflow
I work every day on InDesign CS5 &amp; CS6 documents in real time, stored on GoogleDrive and DropBox to an iMac, Mac Mini and MBAir, all SSD-equipped. My Drive account is provided through my employer, while DropBox is my own personal account.

With a fast internet connection, the syncing is invisible. Granted, files are copied locally, but you can define the location of the Drive and DropBox folders to be on external local drives instead of the internal drives if you wish. Both Drive and DropBox allow for selective folder syncing as well, so users can set their machines to sync only what they need to work on.

For external disks, I would recommend USB3 &amp; 7200RPM HDDs at a bare minimum, with Thunderbolt and SSDs at the fast end.

Alternatively, if the task computers can be upgraded with large internal SSDs, that may solve your problem.