R9 290 / R9 290x
Well, well, well. I can say one thing: R9 290 ROCKS! I mean... really, this thing is a BEAST! In Windows I can play Crysis 1 and 3 at ultra quality settings and is like... I don't know, hot knife through butter. And the noise ain't that bad, I used to have a Gainward GTX 260 GS that was always running loud and hot, up to 90 degrees (Celsius) so probably that's why there is no difference for me from a noise/heat point of view. The performance is phenomenal for $470 (Europe). A GTX780 (which the R9 290 beats in almost every game) is around $600 so it made no sense to buy it.
Coming to OSX support, I'm sorry to tell you guys that at the moment of writing this (15-Nov-13), there is no support for R9 290/290x. While the R9 270x and 280x are kind of re-branded 79** cards, the R9 290/290x are based on a new architecture. Unless Tony & Co. come up with some sort of workaround, until the Hawaii architecture is supported by Mavericks (if it will be) we're pretty much out of luck. I believe full resolution is possible with these cards but QE/CE remains unavailable for the moment.
Prove me wrong, but that's my experience so far.