There are more differences than the fan. If you are watercooling, GET A REFERENCE PCB. I can't stress that enough. Otherwise the waterblock will most likely not fit. The Gigabyte card and the Sapphire card both have non- Reference PCB's (The board in which the cooler is on, in which the waterblock will go on).
If you are planning to watercool, you won't be able to find a reference 7970 Ghz. Just pick up a Diamond 7970 non ghz and you can watercool it. Reference based PCB's for AMD also tend to overclock better and have better power phases.