seriously 275 for a used 780 really isn’t worth while. I personally don’t pay more then 60-70% of the cost of new. get a 290/290x or cough up some more and get a 970 if you want nvidia.
What game or test is that in? When was it tested? Who tested it? Right now I'm completely disregarding that chart. All those numbers value is determined by what game is being tested, the testing methodology of whoever is testing it, and what driver version was used in the tests.
i would go with the Sapphire 290 TriX OC anyday of the week, because its cheaper, and performs better then a 780 now days. Next to that it also has more vram. Hence even the 290X has dropped in price allot lately.
as @Rudster says, dont grab a reference 290 (x), but pic something like the Sapphire 290 (x) TriX OC or VaporX. These are great cards.
This is probably too late for OP, but having built two 4690k systems, one with a 780 lightning and one with a 290x lightning, the 290x when cooled well destroys the 780. Get a vapor x or lighting 290x and you're set for a while.
AMD's compute performance is significantly better than Nvidia's due to slightly less severing (for favor of pro cards), so there is also that.
If it is a reference card... Even my AMD-fanboiness tends towards Nvidia. Unless you are going to install an aftermarket cooler, like I have with watercooling, then there is no reason to spend even $9.99 more for a nice reference cooler that Nvidia makes you buy.