I've just recently fixed my Sansui 881 going into a pair of Realistic Optimus 5. I also have a pair of Optimus 5b and I wonder what are the speaker placement options if the speakers are in the same room?
You're going to need to try it and see what you think. Each pair of speakers is going to act differently. Then add to that the varying room acoustics and it gets even more difficult to predict what's going to happen.
I recently auditioned 2 pair of Rectilinear III's. Side by side they were absolutely jaw dropping. Stacked? They were a mess and went 2 dimensional within moments. And oddly enough, the bass was so pronounced I had to knock it down via tone controls. I can't ever remember having to turn down the bass. It was that bad. I didn't try the 4 corners of the room, so I cannot speak to that.