As you might have understood, I am working with fairly large projects - and one thing that could improve the performance of computer is better graphic cards when it comes to problems in OpenGL. But at a certain limit even on my laptop the program chrashed and deleted 3 stories and left only a small basement floor. Luckily I have trained my 6th sence after advice from Der_planer and I had a recent backup copy of the project, so I didn't loose much. Then I realized that maybe I should delete all assisting geometry (architect plans) and now I am almost finished with all 3 stories + roof of this quite big house. Well it is still a little heavy in OpenGL but yet much better in the design modules.
I think a problem is that DXF is so heavy as it is. One example is a architecture plan that is 2,32 MB in DWG and converted to DXF it is 24,8 MB. So of course the building model becomes heavy when having 4 of these plans...
My suggestion for further development for Dietrichs is to do something about this. The smartest thing could be to be able to use DWG directly, both in import and export - because the connection to AutoCad is also a bit weak - and in some cases you have to exchange information with "AutoCad people". Another possibility could be - t.ex. in coorporation with AutoDesk - to develop another drawing file format that is even lighter than DWG. Then when you import a dwg the Dietrichs program automatic converts to this "lightweight dwg" format. The same at export, so the exported result is dwg.