And about black screen...
To properly boot osx on Dell M4800 must be SMBIOS configured like this:
In Osx El. Capitan, Yosemie or Maverick, the SMBIOS in Clover is configured to Macbook Pro 11.3 or iMac 14,2
In Osx Sierra it must be iMac 14,2.
With Macbook Pro 11,3 cause black sceen.