My lents are extremely pushy and I wouldn't put them in with more peaceful stuff. I had to move some of my large male severums because they were getting pushed up into the top corners of the tank. The only fish left in the tank with them are a giant H. psittacus, a spawning pair of Atabapo severums, and a male Saxatilis pike. They constantly challenge the other fish in the tank. As soon as the Atabapo pair release their fry, the pikes barge in and attack the parents, then eat all the fry. Once every week or so I come home to find my severums all beat up from trying to defend their brood. I definitely wouldn't try these particular pikes with anything like discus or mellow SAs.
I guess it really boils down to not only tank size, but individual temperament. All cichlids vary in behavior and aggression. It just so happens that my two lents, which were pretty mellow for their previous owner, have taken advantage of being top dogs in my tank and quickly attack anything that tries to venture too close.