Well, I have only had my tank running for less then a year...
But, I have montipora digitata that has tripled or qradrupled in size in just a few months.
I have a montipora cap that has doubled in 4 months.
I have an acropora sumpin or other that hasnt grown much at all - half a centimeter? - in 3 months, another acropora (green one) that has doubled in size in a month... etc.
Maybe if you could pin down what types of coral, people could maybe make an estimate
