The 780 Ghz Edition I have and can overclock the memory upto 7000Mhz and the CPU up 40hz. Or 60mhz and 600mhz memory. I find the later more stable. When it comes down to it, the card is the highest factory OC production out of the box 780 and tie up with the 780ti reference card (approx 3%) away. Anyways - the 970 Gigabyte is out now which is bascially the Gigabyte 780 Ghz Edition with overclocks. When overclocked and these overclock allot better the Gigabyte 970 beats the 290x/780ti and is just shy of 4% off the 980.
Now the card of the moment is the 970 cause of its price tag! Its a no brainer. 780ti performance with 4gb and then some at £299's.
If you are doing UHD (2k) gaming the card is perfect, however 4k you will need 2 in SLI to get decent frame rates. The 290x 4GB will be dropping its prices now and the 770, 780 and 780ti have been now discontinued.
I myself will be buying a 970 as I just bought the 780 and am returning it as I am within 30 days. Makes sence!