I have 3 Rosy Barbs and 4 Tiger Barbs in my 20 gallon tall and I hope that they do not grow 5-6 inches. I understand maybe 2-3 inches.
I find that my Tiger Barbs are much more aggressive than my Rosy Barbs. I have cories in my tanks too and the Rosy Barbs do not even bother with them. On occassion the Tiger Barbs will check out the cories, but usually will leave them alone.