You should be getting 440 h/s by default on Vega56; 520 h/s optimized. With a VBIOS modification, you'll be hitting around 630-640 h/s.
Your hashrate will be heavily dependent on your cards voltage (and thus, temperature).
What will it do with 1385Mhz @ 0.855 V (temp always stays under 67*C).
Any details on how much power those 630h/s need?