Id say now that the 7XXX series drivers are updated with Mountain Lion, and Ive had no problem with my 7970 in Mavericks that AMD's new cards should be a safe bet. I would even go so far to say (since everything I have read has indicated out of box success, and my 7970 worked without any alterations) its safe, and to get it, if thats what youd prefer. Just make sure there is a good return policy!That way the worst case scenario is you have to return your card if it doesn't work out of the box, or if you cant figure out a fix that your comfortable with.
I didnt have to do anything at all to my 7970 to get it running last week, and so far its sailing along smooth. Ive had no hiccups, and no sleep problems since I switched to Mavericks. Also since I switched to Mavericks I dont have to adjust the internal graphics. Although i'm not 100% that everyone is going to have the same luck with their 7XXX / R9 series cards, I am pretty confident that they are pretty much ready for purchase and install with Mavericks, and otherwise approved hardware. As long as you get a return warranty there is nothing more than a shipping charge to lose.
But now that Nvidia has lowered their prices significantly on their GTX 780/ 770, not to mention any additional discounts or game deals, its worth taking a second look at your options. The 780's performance compared to the 290X is close in alot of areas. But the 780 holds the additional benefit of a definite compatability, and a lower price.
Currently Im trying to decide whether I want to get a 770 or a 280X. I think that damn reference design on the 770 is undeniably incredible, and I love the certainty that comes with getting a hackintosh, but I also think I want to play with AMD's R9 series.