Maybe a little late but Let me chime in again.
LIke I said I have a six-line and royal gramma. they pretty much left each other alone. Then Friday I got a clown buddy for my percula (actually got a ocellaris cause I like the brighter color) anyhow, the two clowns have been doing the shiver in front of eachother to do the "whose gonna be female" thing. Since then the six-line and gramma have been going at it. Not nipping, but showing dominence for territory. This also might have a little oe maybe a lot to do with the rock work change. So long story short, not only will their aggressiveness depend on the fish, what other fish are there, and even your rockwork setup. It'd be a toss up if I had to pick between the two. My gramma is out a lot more than the six-line, but its fun to watch the six-line room around, in, and through the rocks
Oh, and I have 3 PJ in my 38G, I don't know, they're neat looking, but kind of boring. Maybe they'd school better with 5, but the 3 aren't always together, and when they are, they just kind of, stare....