Oh boy, here we go.
In my experience, Panthers (And Groupers in general) are fairly peaceful, even when quite large. They are eating machines and are capable of eating things larger than seems possible. I've never seen an overly aggressive Panther. As adults, they do like to have a little space around them and will defend this space but rarely persue a tank mate across a tank to defend their territory. Sorry, I disagree that Panthers will kill their tankmates. Just my .02.
As for size, they get fraking huge. However, they aren't swimmers persay so IMO, a 90 is not out of the question. They tend to lumber rather than "Swim". I think this needs to be taken into account when advising on tank size. Flame away, I can take it.
Juv Panthers are really cool; they get ugly as they grow but again, this is just my opinion.
I have little knowledge as to their breeding habits.