I ran my own tests on this issue and found the following
1) The DXF File output from TBC v5 are for sure much bigger than in BC-HCE 4.12 - I have created test files and sent them to support for review and comment
2) The issue that people are raising relating to DXF File Exports using the SCS900 workflow not opening in or opening in and freezing in AutoCAD I have not yet been able to reproduce that, I am going to take a look at Pat's Data next to see if I can recreate that with that data set.
Alan