I also have a SP31 that won't give more than 4.7Th/s. I am beginning to think this is the maximum, a far cry from the advertised 5.5Th/s.
My unit is running @ 240v and close to 3Kw.

•    The hash rate of the SP31 will be 4.9TH/s +- 5%. Power consumption will remain the same 3kW at the wall as in the previous SP30.