For me RX470 Nitro+ OC Hynix is best. Hynix > Elpida > Samsung. Hynix can get 29.7, no matter ASIC quality always get 29.7 at 1150/2050. Then Elpida 29.5 at same clock and Samsung 29. http://i.imgur.com/jF7iGSH.png
What voltages do you have for core and mem and what power consumption?