@burnin
Yes, in the task manager it hits the top and cpu performance is minimal for hours. In the end I was able to render the images (with more RAM + tiled camera). And I know it is an overkill. But some clients are very resistant to advice, even when confronted with hard facts.
@cecofuli
Good advice, too. Forgot about that one. Thanks.
So, as I see from your replies, this issue with hi-res renderings won't be treated in further versions and should be taken as a giving?