I do have the XFX 7970 BEDD. Good performance, even thought it's not the GHz edition.
I understand the 290X cards still have a lifetime warranty with XFX, which makes it a front-runner. If only NewEgg had also discounted the 8GB version.
If you look at the performance of a 290X (Uber = 1Ghz clocks on a reference card) in AT's latest review, they have a
925mhz 7970 on their charts vs. the 290X in a wide variety of games. This gives you a good point of reference as to where you'd end up.
You can also look at just averages
here or
here. Beyond a $253 R9 290X, in this particular 28nm generation, price/performance falls off a cliff. $300 390/970 aren't faster, $450+ 980
max overclocked is only 25% faster, $550 Fury is also about 25-27% faster, $650 Fury X is 32-34% faster compared to a 290X. None of these cards make sense imo against a $253 290X for 1600P. If you want a lot more performance in a single card above 290X, 980Ti @ 1.4Ghz+ is the way to go but it costs $650. I wouldn't recommend you to purchase 2x 290Xs at $250 either because at that point, I think the 980Ti makes a lot more sense as CF doesn't work in all games as well as a single fast GPU would.
I think you have 3 main options:
1) Buy a $250-300 card like the 290X/390 and use it as a stop-gap card to use for 1.5-2 years and then upgrade again to a 16nm 8GB HBM2 GPU (or something along those lines);
2) Just wait another 6-12 months and get a $400-500 16nm 8GB HBM2 GPU in 2016 and coast on a 7970 until then.
3) Just bite the bullet and get a 980Ti now.
If you can find a buyer for your 7970 for $120-150, I would upgrade to a 290X to give you a bit of extra performance while you wait for much more powerful 16nm GPUs to come down the pipe in 2H of 2016 and 1H of 2017.
Of course keep in mind that a $699 780Ti's performance was practically matched by a $330 GTX970 just 10 months later. So if you do decide to go all out on a 980Ti, just know in advance that next generation GPUs will have a node shrink + new architecture + HBM2 8-32GB of memory = one of the largest jumps in a while. That's why a $250-275 card like the 290X is very appealing since it doesn't cost that much $ as a perfect stop-gap card.
Sorry that my post is long as I am giving you more info to help you make a more informed decision. I suppose another option you could consider is finding used after-market 290/290X cards and selling the 7970. That could also work if you can find something like a Sapphire Tri-X 290 for $180 or so and get 2 of those.