Hi OP,
In my humble opinion,
The main question you should ask yourself is what resolution you'll be playing games and/or watching movies. if it's only a 1080p resolution then you're totally wasting your money.
The bottom line- If it's 4k you're after then go for the R9 295x2 option, anything under (like 1440) ... I think you'll be fine with a single or dual 980 GPUs or anything less.
2 R9 295x2 would be a huge overkill and a total waste of wattage and money (you could use the money you save now for later on when both companies release better power efficient gpus and better performances as the Maxwell series is out with a huge energy saving deference while maintaining high performance such as the 970 and 980 cards).
For example. a single 980 TPD is (only) about 180 while the R9 295x2 is about 425 (or 500 as stated on the product's page). Unless you're buying a 4k monitor, I'd advise you to go for a single 980 card, and then buy another 980 when the prices go down when the new cards are released. If you've considered 970 SLI ( limited to Tri-SLI), the 970 SLI seems to be faster up to ~1600p ( a 970 is only 10% worse than a 980 card, and a lot cheaper), then 295x2 passes in 3 display and 4k. . I read on an anandtech forum review ( that tested R9 295x2 CF- don't remember which one) that a dual R9 295x2 is getting 40% bottleneck most of the time (even on the newest Asrock Motherboard the PCI v3 lanes bottleneck this about 40%) so keep that in mind And also they used a 1350 PSU and it shut down on them several times due to not having enough power) .
About your comparison:
A pair of 295x2s in Crossfire is basically a 4 GPU setup and that will beat out 2 GTX 980s. However they will consume about 3 times more power minimum and you'd probably find that 3 GTX 980s in a 3-way SLI will probably be as good if not better due to non-linear scaling (don't quote me on that though, I haven't actually seen any benchmarks so I'm only hypothesizing).
You might as well ask yourself - Which one would do better for QHD triple monitor setup (the r9 295x2 vs the 980)?
Both are really close in performance.
Depending on which game you're playing, for instance the 290X crossfire is a tad slower than 980 SLI.
From one 980 to SLI it's about a 40-50FPS increase.
Even though these are for 4K resolution, you still would be better off with GTX 980s.
Or Bioshock where 980 SLI is still faster:
But then you have Crysis 3 where It's basically unplayable.
Word of warning:
Regarding the R9 295x2 : I've been hearing that connectors actually melting . Do not use daisy-chained PCIe power connectors (i.e. one connection to the power supply and two 8-pins to the graphics card). If AMD wasn't going over the per-connector power spec it wouldn't be an issue, but they are, which means you can melt the connector at the power supply end. Those daisy-chained PCIe connectors are meant for 300W max, not 425W, this is the *only* card on the market that causes these kinds of problems. If you don't know what it means - well basically it's how many CABLES from the PSU you're plugging into your GPU (6/8 pin cables) - sometimes you can have a single cable with two pcie connectors on the end, one daisy chained of the other. Don't use connectors like that, use two individual cables instead.
Also, you’ll need a serious and quality PSU (or dual PSU if you have the right chasis – at least 1475W or preferably a 1500W) to run 2 R9 295x2 .
I hope I helped.
Good luck.
I already had them. 
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