Woah. What an ordeal. I've been using this mATX golden build from Mavericks (I think) upgraded to Yosemite. These past few months the whole thing has just been slowly and steadily getting slower. First major issue was Powerpoint, files especially big ones eg 300mb would take 5-10 minutes to load. Initially I thought it was the Office Live I get from work, and so I installed Office 2016 - marginally better. The installation took a whole day to finish, when I could install it in 10 minutes on a 2010 Macbook Air (that was acting as my OSX stand-in whilst I tried to refresh my hackintosh). Disk scans, permissions etc did not help the slow transfers. So in the end, I thought I needed to do a clean install with El Capitan.
First, difficulty getting hold of El Capitan. Then making the Unibeast USB literally took hours. First install seemed to go ok, then on rebooting, my dual screens connected to my GTX760 went blank, and rebooting didn't help. I couldn't get the system back.
So tried to use my MBA to make a new USB, but since it was already on El Capitan, I couldn't download it again. Cue all sorts of attempts including BT. But new USBs (which again took hours) wouldn't boot - despite all sorts of boot order shenanigans. In the end, I flashed the BIOS of the MB. Now I got my UEFI option back on the USB, and then it booted. But rebooting, hell - black screen again. Try the internal graphics I thought, so I unplugged the displayport from the 760 but before I could find the DP on the MB, the single HDMI screen came back on. And when I just replugged the DP back into the 760, both came on. Hallelujah.
So now I'm back online. I even have sound despite not expecting to from some posts. Gingerly I'm setting it up again.
Anyway, TLDR, big ordeal but couldn't have done it without Tony's site. Big thumbs up. If Apple would just update the iMac, Pro or even the mini, I'd have swapped out my Hackintosh for an official machine this past year. Now, I'm hoping this will hold until the Surface Studio is available in my country.