What are some small to medium sized aggressive new worlds that wont get bigger than 9" ? Stuff along the lines of Convicts, Blue Acara, Neets, and Salvini.
If you want something truely aggressive you can go with a grammodes, but they are extremely slow to grow. I was quite astonished to see not one but two full grown adults.
A male Dempsey much over 9" is a rare site. Yes it possably could go over 9" but it would take many many years if it did. It's like the 16" Midas or the 24" Dovii or the equally allusive 20" Jag ok maybe not that rare but you get my point 12" Dempesys aren't fall out of trees.
assuming you want to be sure to stay under 9", I'd skip the GT and put a "maybe" on the Dempsey . . . I don't think Blue Acara or Firemouth are particulalry aggressive, but there are exceptions in every breed
Salvini would be a nice choice . . . colorful, nasty reputation, and likely to max-out at that 6-8" sweet-spot . . .
100% true, but since the OP asked about "small to medium" cichlids, I don't see why we would suggest fish that are on the larger side of medium . . . there are a lot of great choices that fit in his range, without pushing the envelope . . .
or running the risk of inadvertently buying a male JD/GT that outgrows his setup . . .