Well. Do not quote me but articles claim they are clocked above the point where reference models fail. It is possible that tweaking the memory clock up more and the core clock down may squeeze more hashes with less watts, or so people here say it is about the memory clock more than core.
I would expect these to outperform the reference models. My main concern are custom bios flashes. I do not know if these will work with the reference ones since those are now based on rerouting power due to the limited 6 pin connector, something that these cards are not restricted to.
If someone who knows about the bios for cards with different factory overclocking and PCB could chip in, it could clear some stuff up.