I can never recommend a fh in a community tank. Maybe with non cichlids but definately won't work with weak cichlids like jd and green terrors.
About the same, expect an inch a month. Oscar and fh are not at all compatible. Oscars are slow and clumsy and weak. The flowerhorn is going to notice that immediately and be on him until the Oscar is dead. It doesn't matter how large your tank is.
Old world, New world, FH world.