I'm assuming 480GH is the desired aggregated speed from at least 4 units? That's about 275MHz, which is pushing pretty hard. Some people reported taller feet and under-board airflow helped increase stability. The actual limit on this board is thermal derating of the main regulator, which is the rectangular add-on board in the corner by the pot. Keeping that cool will also help.

Yes the fans on these are pretty crappy and I won't be using them again.