I would like to upgrade my gpu and my choices are either gtx 780 or r9 290x both on ebay can be foing for simmilar prices. My

I'll second the 290x as well. Nvidia quickly drops support for their cards once they are no longer the big money makers. 780 owners have worse performance now than they did a year ago. Plus the 290x beats the tar out of the 780 at resolutions higher than 1080p thanks to it's larger memory bus and quantity of memory, two things that will become increasingly important now that we are moving to video cards with HBM.