I wouldnt go with a sailfin in a 75 reef. Maybe a 75 FO tank. But i dont think in a reef he is going to have alot of swimming room IMHO. They arent as susceptable to ich as other tangs such as the purple or regal tang are. But they can still get it just like any other fish. IMO tangs are high maintenance fish and the owner should have enough time to devote to taking care of that fish.
HTH
aaron