For all the haters on Elpida memory out there:

Featuring RX 470 Nitro 4Gb:

EDIT: This is sporting sony87 ROM so all the credit goes to him!

This probably says more about RAM cooling than it does about Elpida/Hynix/Samsung performance.
http://www.kitguru.net/components/graphic-cards/zardon/sapphire-rx-470-nitro-oc-4gb-review/2/

Or more about the ram timings and acceptable Tcase for those timings

Nice overclock by the way - Congrats