Problem 4: Black screen when using iMac15,1 or iMac17,1 or MacPro 6,1 system definition
Fix: modify the AppleGraphicsDevicePolicy.kext as pointed out by PikeRAlpha here. We have two options, using Clover's built in kext patching (preferred) or manually editing the kext. Using Clover to patch the kext on the fly is preferred because it does not get over written after each OS X update. If you do it manually you will have to make the edits after each update.
Method 1: The easy method
Use KextBeast to install these two kext Lilu.kext and NvidiaGraphicsFixup.kext into your Library/Extensions folder.