I got 120Hz working on Hawaii. Its a little finicky though. Its with 2 Club3D 290X's and 5 Asus VG248QE monitors. And not all the Asus VG248QE likes the 120Hz. A couple of mine refuse to work while 2 of them work no problem.... Strangest thing... I had to use Toasty's CRU thingy to get it to work. I have 2 hooked up DVI, 2 going through a Club3D MST hub and one with a HDMI to DVI-D cable I got from Cable Matters. I was going to get a HDMI to DP cable and see if that helps out at all but haven't done it yet.
If you want proof I can make a Youtube video for you.... 100Hz works all day long without any problems except one of the monitors keeps telling me I am using the wrong cable so I got to turn it off before I game which is a pain in the butt... But thats what you get for using bleeding edge technology. I might be testing the new 290X2 or whatever they are going to call it. I heard it has 2 DVI one Dual link and one Single link and it also has one mini dp and one full size dp. It might be able to push 144Hz using 2 Club3D MST hubs and the dual link DVI. This has yet to be confirmed. I have not seen a picture of it just read about it in one of the leaks.
In this video the 5 monitors are running at 100Hz.