Thank you RS for the detailed reply. Running through some costs, 2 more monitors will cost me US$ 1200, and while I could get by with a single 290x, (knowing me) I'd want to upgrade to a new-generation card, easily another $700 or more! so I'm looking at spending ~$2000
Is there going to be a single card solution in (late) 2016 that can power 7680 x 1440 you think?
Technically speaking you can power those screens with a single 290X and play games with reduced settings. Since I can't accurately predict how much faster 16nm GPUs will be (50%, 70%, 90%?) and more importantly how much more demanding future games in 2016-2018 will be, my train of thought for 4K or multiple 1440P panel users is:
If you want to play in the elite leagues with 4K, 5K, 8K pixels, the cost of GPU upgrades should not be a factor. If you want the best experience, you'll need the best GPU hardware for it.
That would be my own personal train of thought but everyone is different. As you outlined above, you'd have to shell out $1200 for just 2 monitors but remember during past GPU generations how quickly modern GPUs would become outdated on a single 2560x1440/1600 screen? GPU progress has slowed down where now GPU performance roughly doubles every 3 years while in the past it was common to see doubling of performance every 15-20 months.
If you want my honest opinion, if I wanted a large screen, I'd just buy a 40-48" 4K TV/monitor and not bother with Eyefinity. I think Eyefinity is awesome in racing games but for the rest I'd much prefer a single large screen.
I am not sure I answered your questions but I think next generation a single GPU should be at least 50% or even 70% faster and your goal would be far more achievable. I definitely think Big Daddy Pascal overclocked should in theory come close to Fury X CF/980Ti SLI. Maybe you can hold out and see what's up and perhaps rethink the entire Eyefinity scenario and go large 4k screen.
The reason I say that is the Titan X (an after-market 980Ti is even faster) is very close in performance to 780Ti SLI at 4K:
At the same time, we don't even know for sure when the flagship Pascal (Big die) is launching, is it 1H 2016, 2H 2016 or will NV release 970/980 successors and push 980Ti's true successor to Q1 2017? Hard to say right now since the rumors are too scarce on solid info. This is why I recommended you getting a used 290X in the meantime if you need more performance to hold you over until next year.
You know if you want more peripheral vision in BF4 and World of Warships, perhaps another alternative is a 3440x1440 34" monitor. Have you used multiple monitors before for gaming?