Are you sure your elpida memory is running 2200mhz from 1750mhz stock , I do not see elpidas to go so high , you have to use some very loose timings. With eliovp elpida strap you get at 1150core/1950mem about 28.5+ mhs eth , higher clock the memory higher the hashrate.

On some 470/570 4gb elpida 1750 and 2000 straps are the same , using eliovp strap which is based on 1500 strap ( with some small changes ) on 1750/2000 straps will give you boost to go to about 30mhs depends of the lottary how much high your memory clock without errors.