They went pretty far in Oblivion aswell, I guess you can hit them with a lot of skill. It ain't going to be easy.
I was able to hit enemies outside the detect life radius of the gray cowl. Longer would be possible but hard as the target become so small and you had to aim high.
Spell travel in a straight line so you can hit targets even longer away.
Long range sneak attack with poison would be a nice way to take out dragons, so nice I suppose they have poison resistance.