Bollo3532 :
hotter-than-Vishera :
Bollo3532 :
turkey3_scratch :
The 290x is barely an upgrade from the 780 - it'd be a waste of money. I'd get another 780.
In most games yes it is barrely an up grade but in witcher 3 the bench marks are showing it is almost 50% more. For example one bench mark showing 1080p the 290x gets 47 fps but the 780 only gets 32. A 50% incrase would be 48 so it is almost 50%. I am not sure how much better a second 780 would be then a 290x. Here is the bench markhttp://api.viglink.com/api/click?format=go&jsonp=vglnk_143303835976611&key=4d2fc1107481092ac96eb10f8fa4bc15&libId=iabsteh80100qcm0000DLb1minfj7&loc=http%3A%2F%2Fwww.gamersnexus.net%2Fgame-bench%2F1947-witcher-3-pc-graphics-card-fps-benchmark&v=1&out=http%3A%2F%2Fmedia.gamersnexus.net%2Fimages%2Fmedia%2F2015%2Fgame-bench%2Fwitcher-bench-1080-u.jpg&ref=https%3A%2F%2Fwww.google.com%2F&title=The%20Witcher%203%20Video%20Card%20Benchmark%20-%20Poor%20Software%20Optimization%20by%20CDPR%20%7C%20Gamers%20Nexus%20-%20Gaming%20PC%20Builds%20%26%20Hardware%20Benchmarks&txt=
What's your CPU and motherboard? Let's remember, too, SLI scaling. I think the 780s get 50-60% in dual SLI scaling, so getting a 2nd 780 would be the same as getting an R9 290X if the benchmark is correct. But a system with plenty of PCIE lanes or a good CPU would scale SLI better, in theory.
4670k in an asus maximus 6 extreme motherboard
So that means that the SLI scaling will not be too much, probably about 50%. However the GTX 900 series has been out for quite some time now, and the GTX 700 series is largely phased out. For example, on Newegg, you cannot purchase a new GTX 780 anymore. They are all refurbished or open box. So regardless you probably don't want to get another 780, getting a different card will be a must unless you don't mind refurb'd models.
Most reasonable R9 290Xs go for between $300-350. With that in mind, you might want to go for a GTX 970 as it's a more modern model with better heat dissipation and power consumption. Also we all know how The Witcher 3 is a lot more Nvidia-friendly than AMD-friendly. For this case the GTX 970 may be equal to if not better than an R9 290X, and Nvidia has proven to have better driver support than AMD at any rate in case you want to 970 SLI in the future (which is a more cost efficient option than a GTX 980), particularly in multi-GPU setups. So I'd urge you to consider the GTX 970, although the R9 290X is not inherently a bad choice in this case, either.