From some of the sites I follow, it looks like Bclk is the way one must go.
It looks like the motherboard is key also.
In the youtube video, it looks like they get 2632Mhz from their DDR4 memory.
(in the Anandtech article, skip past the maniac who uses liquid nitrogen to over clock):
https://www.youtube.com/watch?v=MrfTcXQlsbs
http://www.anandtech.com/show/9848/b...rs-coming-soon
http://www.eurogamer.net/articles/di...be-overclocked