Has anyone known an ACD/GS mix?

My Luna is 7 months (Red Heeler), and our Neighbor's pup, Gatsby (German Shepherd) is about 6 months. I know it's too soon to be talking litters but neither have been fixed yet and we were discussing the possibility of letting them have a litter before doing so. They get along very well, inseparable, and are both beautiful dogs. Not like paperwork pure breeds, but both shining examples of the behavior and intellect one would expect from a classy certified pup.

Does anyone have or has anyone known anyone who's had a German Shepherd/Red Heeler mix? If so, what can I expect in size, behavior, so on.