Oh I believe it, IMO RD are the most pure aggressive fish out there. (They don't need a mate to be nuts is what I mean.)
Yours is right at that size where it should "snap" as they call it and become a real glass banger.
When I had mine he went crazy at about 5-6" and that's when all the fun with this fish starts. WC's become waaaay more interesting that's for sure.
Good luck with it, at that size it should start bulking up and then hit another growth spurt. Between 6-7" mine added what looked to be another pound just getting thinker and then shot to 10-11" and started to bulk up again.