Very low hashrate on two 770s

I am trying to crack a lost mac password hash but when I load the hash.txt file into cudahashcat I am only getting about 7000H/s, 3500H/s per card. Here is the command I am using (I open a command window in the folder directly)

cudaHashcat64 -m 7100 hash.txt -a 3 ?a?a?a?a?a

What can I do to speed this process up?