I live on the other side of Austria, in Vorarlberg, can get the
Sky channels on a sky minidish, and I even get the weaker 2D channels (ie BBC, ITV ...) ca 50% of the time on the minidish! 80cm dish guarantees the 2D channels, you migth lose then still during the odd thunderstorm though.
Vienna will be a different story though for the 2D channels, as the footprint starts to fall off rapidly as you cross Austria. I agree that 1.8M would be minumum you would need. But, you will still get the 2A and 2B channels on the mindish in Vienna!
-Wally