Well, i use a lot of downscaling in my game and i always like to work on a project with all setting set to high level, Because,
A. quality is good
and B. So i'll know i am pushing the limit while i am optimizing the game, then if i need more power i can always using lower setting.
My game is targeted for PC/MAC/LINUX so there is enough power to go around and i didn't notice any droppage when switching to high quality downscale.
Anyways I'll switch back to medium.