Want to give props to tiimp for his post. I also got the Asrock z97m-pro4. I used a nvidia GT 640 with 2 gb for video. 12GB of ram with missmatched modules (know that is a no-no but it was what I had and I have it all clocked to 1680 which works just fine). 256SSD from aData and an i5 4670k overclocked to 4.2ghz without problem. I'm running 10.10.4 by the way. Started with 10.10.1 on the Yosemite install cause that is was I had. Was able to do a very simple auto update to 10.10.4 after I was done. NOTE!!-AFTER doing the auto update to 10.10.4, my EFI partition was no longer active and I had to boot from the USB. Had to run through the last part of TonyMac's EFI tutorial (starting with step #5). The update didn't corrupt the EFI at all. So all you need to do is make it "active" again. Perhaps you can do that before rebooting the install. Not sure, didn't try that.
I did not have to put in -x or -v to get OS X (10.10.1) to boot from USB. What I did have to do is use TonyMac's "Extra folder to EFI partition" instruction sheet. That was essential. Best I can tell it's something about the SSD. Without doing this EFI, the drive was never bootable without the USB for me. So it's essential. The boot0 thing is only a problem if your boot drive is 1TB or bigger. Found this out last time. I had a 2 TB timemachine back up and a 1 TB older drive that I'm using to 'serve' my media (movies, music,pictures) to my faster SSD. I had these and a 500mb HD that holds windows 8 all hooked up during the process. Not a problem as long as you keep everything straight. If you think you'll get confused then disconnect as is recommended. You don't get boot0 for connected drives that are 1+TB. Only on boot drives of that size.
Additional comments...
1) Had a problem with LAN originally but using the Intel Driver tiimp mentions should work. It is working fine for me.
2) Sound- This one was weird for me. One poster stated that the ALC892 worked fine. I tried repeatedly to install it with multibeast but never could get sound working. I wasn't sure what to do but ended up finding a turtlebeach USB AMIGO II on ebay for about $8. Figured it was worth it. When it came I plugged it in and all of the sudden a whole bunch of audio options appeared. I swear they were not there before. There were 3 "line out" options and a "digital out" option and this was after I removed the AMIGO II. I'm using simple line-out and the first option was the one that worked fine for me. I haven't tried the digital out but am curious about that. This is not an HTPC so really don't need anything more than stereo. I'm puzzled as to why they showed up after I plugged the AMIGO in. I have rebooted multiple times now and the audio is still going strong at this point. Glad I only paid about $8 for the AMIGO as they go for $25 brand new.
3) Overclocking with this board isn't quite so straight forward in my experience. Maybe in Windows it works better but it seems that the auto Overclock options aren't well tolerated by Mac OS X. I had to do the basics by hand. But I did not monkey with the voltage and other fine stuff. Left that as "auto" and it works fine. I have a liquid cooler, cosair H60. I turned speed step off and I think I disabled turbo. With "turbo" running the chip is held at a lower level. I'm not sure if it will ramp up to my max with work load.
4) Stability - Every once and a while OS X hangs at the end of the boot sequence. I have to reset and generally it boots fine after that. Nothing is ever bothered by it and once in OS X proper I haven't had any problems. It also doesn't seem to tolerate 'sleep' very well. I've set it to "never sleep" status and that is fine. Some times if I put it to sleep manually it does fine but somewhat temperamental. This isn't new to me. Sleep hasn't really ever worked real great with my hacks.
5) Overall I'm happy. I would say I'm not sure how snappy it is. I thought it might be quicker but it doesn't feel that quick. Probably just my bias. This is my Third Hack now and I'm quite happy.
Thanks to TonyMac and all the enthusiasts that keep this site rocking!