My 7870s run at 80% with 2 WUs. While most seem to say more than 2 shows no advantage it would not hurt to try. The 7970 is power house.

Everyone says you need 1 core per WU. I tried it in the past and saw no difference. Tried it again with different hardware, let 4 GPUs on 2 machines have 2 cores per GPU. After 3 days no difference to speak of. Back to .5 core per WU. WCG needs the cores and no benefit for E@H on my setups. Why my GPUs do not see the difference I do not know. I know the people saying 1 core per WU know what they are talking about.

From what I understand memory clocks are the least important on E@H. I read to OC everything else and when at max then up the memory. If you reduced it and saw no difference other things are probably what is holding your GPU back.