It’s really important for you to file a bug report if a file doesn’t load to your satisfaction. This is a secure form: https://unrealstudiohelp.epicgames.com/s/article/How-do-I-report-a-bug
For import of complex assemblies, you will benefit from faster CPUs right now and lots of RAM (I would have thought 64Gb would be plenty, but I don’t know the complexity you’re dealing with). Cores will matter if you’re using Lightmass in your interiors. Lightmass speed is almost linear with CPU cores, probably 1.7 or something. Similar to rendering linearity.
Don’t forget, in 4.20 we have two-pass CAD import, so the first pass just loads the assembly tree, allowing you to make decisions, merge or delete things BEFORE you actually load it. This will save you lots of time and require less RAM.