Hi Paul,
We have tested files upto 180 MB in size and they seem to load well in both the old and new 3D viewers.
The new model viewer can load even larger files, though its in Beta.
Could you please share the ifc files to our Support team (connect-support@trimble.com). We will investigate. There could be other factors that might be impacting the model loading.
Regards
Darshan Kamat