Gus,
The answer depends on how you are planning to use the overlapped models.
Revit files are VERY large and so I am not surprised you are having problems maneuvering in Archicad when they are all in one Archicad file.
If you are overlaying the models for reference and such as clash detection then you really only need the geometry. Your consultants can send you 3D DWGs which are much smaller files but have no other data. Depending on how many facets are in the models they may still be problematic, but try it.
Another solution is to upload all the files, including yours, to Tekla BIMsight or another cloud application which can handle the larger combined models. They have built-in team commenting, redlining, task assignment and tracking etc.
So, back to my question, what are you trying to achieve when you overlap the models?
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"