Just as reference: I am developing in Punch a new "historic house", aprox. 13800 sq.ft., with custom fireplaces, custom cabinets, crown moldings, iron handrails, columns, and lots of details, custom objects, topography, etc. The size of te Punch file (it is almost ready) is 8.7Mb
Other file: Shopping Center, (I developed it in 4 files), with stores, and columns and photo view pictures, etc, each plan with 800 x 800 ft, 7 to 8 Mb each.
In my opinion, what makes difference in the 2D (floorplan) speed is the topography.
Work in a file without topo and insert the topo at the end is the best option
Hope this helps
Patricia