We're not ignoring you. Its just a hard/impossible question to answer. They will all grow at different rates depending on what type of tang, nutrition, etc. We have a blue/hippo/regal tang that grows super fast (about 3inches in 1 year) and a purple who grew 3 inches over the last 4 years. Both the tangs you have WILL outgrow a 120 but how fast?...only time will tell.