I am not sure if 10.9.1 will support Hawaii... Why I'm saying that is because the new Mac Pro cards have Tahiti based AMD FirePro D500 (maybe D700 as well, although not officially listed on Apple's site). Tahiti support is already built in Mavericks so there is no real reason for Apple to add support for Hawaii if they are not planning to release a Mac with Hawaii based graphics. There is one hope though: the new Mac Pro equipped with 2 graphic cards requires some kind of crossfire technology which works without a CF bridge. The only cards on the market that can do that *
on the PC* are the Hawaii based ones. But AMD could have built Apple exclusive Tahiti FirePro with that capability (of running CF without a CF bridge). The hope here is that the D500 and D700 are/will be Hawaii based.
For those of you that do not know what Tahiti and Hawaii are, these are codenames for the graphical processing units used in the video cards produces by AMD during 2012/2013.
So this is for all of you that are planning to use OSX as their primary OS:
do not purchase R9 290/290X at the moment. Go with the Sapphire R9 280X Toxic (highest performing 280X on the market). The performance is between 10-15%(290) 15-25%(290X) lower in most games but it's fully supported by Mavericks. It's still a beast though, so no worries about playing all games under the sun at high quality settings. You could even go with a CF later if you really need to (and that would surpass a 290X by around 50%).
As a side note: if you want your R9 290/290X to kind of work on OSX, you need to install the bootloader and Extra on the EFI partition by following this guide
http://www.tonymacx86.com/401-install-bootloader-extra-efi-partition.html
You will get full resolution through the bootloader (1080p display option in Multibeast section Customize -> Boot Options) but no QE/CE.
An alternative would be to run a second graphic card supported by OSX. I tried that with a GTX 260 but every time I would want to boot in OSX, I would have to change the default init display in BIOS and then change the monitor from the radeon to the nvidia DVI port. Also this had it's downsides: the nvidia cooler kept on spinning at 100% until booting into Windows with the Radeon card (I kind of know what's happening there but no way how to fix it). Then the Radeon cooler would spin at it's default bios setting (47 or 43%) for the entire time running OSX (as well, I kind of understand what's the reason but still no way how to stop it). You might get better results if you try so check this one out if you have the opportunity.