Quote - And how do you figure that, as in order to reduce its size to half, you're throwing information out?

You're always throwing info out when you do a render, as usually textures in a scene are rendered at lower then native rez. So the question of 'quality' is simply that of how good your renderer is at resizing images and AA. FFly is, unfortunately, not very nice at this, certainly a lot worse then Photoshop. So if you render large enough that your textures are near native size then resize down in Photoshop you will get better and sharper results.

But this also means that there is no point in rendering larger then your textures. So eg if your scene mainly has 1k x 1k textures and they take up half the screen, anything more then a 2k x 2k render is a waste.