I would not have the marbles to try 3 clarions ina 180. I would DEFINITELY suggest the 1000 if you were gonna try it. My clarion is very peaceful with the other fish, but has a death vengeance against regal angel, and will deconstruct one in less than an hour (I know from expereince). So, I would imagine that aggression between clarions would be horrific.
That video from Cortesz is very neat, but I wonder how it would last long term. If I presume correctly, that video was very recently after collection. Once territories get established, I would imagine there would be some wars. Just speculating, though.