Ta for the suggestions. I tried the Nvidia settings but they didn't improve over the best I had got.
Re. cotty: CAD stands for Computer Aided Design. If Sketchup is not a CAD program, what is it?
Even so, that's not an answer to my question, which surprisingly not even the resident Gurus seem to know: How come other computer design software is so much better with sharp clean lines than Sketchup? I love Sketchup, would just like it to look as good as is currently possible with 2015 software and computers. Is that too much to ask?