I have a pair of green sevrums in my 125, and the male OWNS the tank. I've got 2 JS'd, 1 'Belly Crawler' Pike, 1 Salvini, and 1 convict. My male sev beats all my other fish with the exception of my larger JD. I bought them nearly 6 months after my JDs and my male is already as large as my male JD. They were purchased (under 1" long) in april and are already 4" long and meaty.
Although mine is an ass, I have had sevrums in the past that were very timid, great fish. The meanest fish I have ever seen was a full grown male Sevrum, he would kill anything in his tank, and try to attack you if you got near the glass.
All in all, i'd say these are wonderful fish, and like most cichlids have vaired personalities.