I have books that put them in the middle of the road with agression. But after four rounds with the species going back to 1995 or so, they haven't shown any kindness to other Viejas.
Even small females can be little terrors. I'm working with a trio now and their going to erupt any day. The females are back and forth on each other all day trying to get the males attention, but he doesn't know if he wants to kill them or breed with them.
On the flip side, I'm working with a group of 5 (2m & 3f) Rio Chacamax Bifasciatum at 7" that to date are getting along great.