Hi all, i like to by me a HD 7970 with a watercooling system, but i am not shure if the Ghz Edition have a reference pcb.

or if XT & XT2 have same pcb designe (by stock)

Well the problem with that is finding a manufacturer who use's reference only designs. And the only manufacturers I know that use solely reference designs is vision tek and diamond. 

With the 7k series this time around AMD gave manufacturers time to develope there own custom PCB / Coolers ect... (hince why you don't see reference cards by manufacturers like Asus, XFX, Sapphire ect..)  So knowing if they are reference AMD designs you'd need to start shooting those respective manufacturers emails. 

But I'm sure you could google it with faster results. Its just something I don't have the time to do at the moment.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814103201&Tpk=Radeon%207970

http://www.newegg.com/Product/Product.aspx?Item=N82E16814129204&Tpk=Radeon%207970

I5 3570K@4~5.0ghz: Gigabyte GA-Z77X-UD3H:Corsair Hydro H70w/Delta 240CFM Fan: 16GB Corsair Vengeance DDR-3 1600: 2 XFX Radeon 7950 @ 1150/1575 : Corsair AX 860 PSU: x2 WD Black 1TB HDD's: 90GB OCZ Agility 3:CL X-FI:Corsair 500R Arctic White Edition:3 22inch Asus monitors Eyefinity @ 5294x 1050(bezel comp) : Alienware Tact-X Keyboard: Naga Razer gaming mouse:Corsair Vengance 1500 Headset .

Check here, and go down to the compatibility chart.  It's not complete, but it's a start.

You can try other water block manufacturers for a compatibility listing as well, though always look for confirmation.  The Gigabyte 7970 OC, for example, had a reference layout in the first revision, but moved to a non-reference layout with the second, despite not changing the product name and model number.  Last I checked, EK still had it listed as compatible.

Another option is to go for a universal GPU block along with passive sinks for the RAM and MOSFETs, which means pretty much any card would be compatible.  Plus, you get to re-use the block on the next graphics card.  The downside is that more heat is dumped into the case from the passive sinks, and they won't do as good a job as a full cover block for VRM temperatures.

In general, Sapphire is the manufacturer most likely to have a reference board design.  Obviously not the case for their 6GB model.