For my screenshots there is not even antialiasing enabled... maybe it looks "smooth" because of a quite high resolution, don't know... in the final game you will be able to choose the AA mode...

Hmm.... 50 cubes is not that much I have 120 bricks lying around in the room, the walls, ceiling, floor, window, door and some other models and I still get 400+ FPS when I disable volume shadows...

Seems that you do something wrong, but of course I cannot tell you what, because I don't know what you are doing there