Yo, Yupi, get a grip -- 7"! (no offense intended) Vlamingii's will push 2' at maturity. I made the mistake of getting a small one (maybe 5") in my 90. I was thinking that their growth might be moderated by the available space -- WRONG. Two or three years later, he was about 12" long with another 3" of streamer fins (who knows, maybe that was moderated growth). He was developing the nice blunt forehead too. Very tough and peaceful fish but already way too big for a 90. I was looking for an appopriate home for him when I had my tank meltdown last winter (no power for 36 hrs.) and I lost him. Very sad day.
You can sometimes do better on juvies -- SWF does run specials on them from time to time. But make sure you have a BIG tank because you'll need it soon.