Here's what OcUK is saying:
Maxwell is an overclocking beast both on core and memory.
Fury you can't clock the memory full stop and on stock voltage Fury does not clock well at all.
So it will all depend on how much more headroom Fury gets from some extra voltage but right now voltage is locked.
For example a stock Ti which AMD compare against is 1000/1075/7010 clocks. Your extremely unlucky if your Ti can't run stable at say 1200/1400/7600 which gives a drastic performance boost.
Example the fastest card on the market right now is the 980Ti G1 by Gigabyte, it's a Titan killer as my one out of the box boost at 1377MHz OUT THE BOX! It can run stable at 1300/1500/8400 and the performance is absolutely insane.