- GTX 970 > R9 390X (http://www.videocardbenchmark.net/high_end_gpus.html)
- GTX >= R9 390X (http://www.tomshardware.com/reviews/amd-radeon-r9-390x-r9-380-r7-370,4178-6.html)
And there are more benchmarks. The 970 has higher FPS (~5 more) sometimes, while other times the R9 has more (tho it's ~2 more). So you could say the're even on the FPS deal.
Conclusion: almost same FPS (depending on game, system, etc), but the R9 power consumption and heat is just INSANE.
I would go with a MSI GTX 970 G1 4Gb