Tough call, IMO. 524 for an OC 780 is a great deal and if 290x releases at 699 I'd say keep it. But if 290x releases at 599, or if you think Mantle will be a big deal, or if you could use the audio crappola (which is one of the things I'm interested in, since I think I'm going to build a new rig for my home theater) I'd probably lean towards returning it and getting the 290x.
599.00 I would definitely be in. hopefully the DBA sound level is quiet at idle and load on the 290X. If there is a 15-20% gain at 1920X1200 then I will be in.. Currently i only use creative sound blaster cards for sound and always will. I do not think I want to upgrade to 2500x res for at least another year. The NEC wuxi2690s have treated me good and do not mine 60hz vsync. When the time comes though a triple monitor setup at 4k res is my next upgrade and by then I am sure I would need to crossfire or upgrade to the next generation video card