For example I had installed ImagineSim's demo version of KATL in order to test its performance. And that was exactly the problem: Got an OOM on the first flight to KATL. Well now you can say: OK, the PMDG777 needs a lot of VAS, as well as AI traffic. But at the big FSDT and FB (and also FlyTampa) airports it works. ImagineSim's Atlanta doesn't look bad at all, but at airports of this size you can see that they hardly work without the abilities the addon manager has - creating and destroying objects on demand. Same thing with Aerosoft's Frankfurt. They always claim they did so many compromises in favour of a better performance (while looking ...well at least OK). But it's still way worse than for example KDFW or even KLAX, even without an ORBX full fat region around it. All this in Prepar3D v3.2 - remember that in FSX VAS problems are a lot worse. All that prevented me so far from buying KATL. Was there an FSDT version I wouldn't hesitate to buy it.
Regards, Dominik