Just to add a bit more content into the discussion, Anandtech has benchmarked Civilization: Beyond Earth with a handful of cards including the R9 290X and both Nvidia 9x0 series, posting average and min fps and the results put the 290X in a very good position, with or without Mantle.

It's a shame that they haven't tested the R9 290.

Xbit Labs 980 test (980, 980OC, 780OC, 780Ti, Titan and 290X)

http://www.xbitlabs.com/articles/graphics/display/nvidia-geforce-gtx-980.html

I mean yeah it seems like once the dust settles the 980 will be ~10% stronger than the 290X. Over time I wouldn't be surprised if the 780 Ti falls to nearly the same performance as the 290X considering its skimpy 3GB of memory (Then again it was only like 5% stronger anyways).

Just thought I would add this:

http://wccftech.com/amd-tonga-xt-r9-m295x-benchmark-surfaces-impressive-results/

The M295X is a downclocked 285X. It beats a full 770 by almost 10% and I expect the 285X to be clocked at least 30% faster. Hell the 285X really might match the 290.

Hope they make a 295X!