OP: The GTX 760 is actually quite a bit below the R9-280x from the benches I've seen, as another poster noted its more on par with the GTX770. In any event, the R9-280x is shaping up to be a real nice low end enthusiast/gamer card. It's about 2-3 clicks below Titan performance for what $269? That's awesome!
Yes, the R9-280x is a rebuilt 7970Ghz edition, but it's looking to be a lot cooler and quieter than the 7970 in addition to carrying the TrueAudio. Check this out:
http://www.guru3d.com/articles_pages/radeon_r7_260x_r9_270x_280x_review_benchmarks.html (best benchmark article I've seen with the new Radeon cards so far.)
Anyway, if your choice is between the GTX 760 and the R9-280x it's a no brainer, get the R9-280x. However, if you're debating a GTX 770 vs the R9-280x the scores are real tight on performance, but the R9-280x really shines in the other "less oft considered" stuff; power consumption, heat, and noise. I think this is a case of newer is better.