73C° seems safe for me, my HD5770 at full charge is at 80-85C° and my HD4850 can go up to 110-115C° (it's mono slot) but only 90-95°C when mining.

The problem is your fan because above 85% of it's full speed, it's durability might significantly shorten.

So it should be better to reduce the fan speed to 85% and see the new temperature.