Hi Stork, thanks.
I Have another Hackintosh with HD4600 and when you connect a VGA monitor, It doesn't make anything. Black screen.
But, in this case, the display is recognised, so I think there must be a way... and then, I've found the solution (google).
Go to System Preferences > Displays and I choose "Best for display" in the VGA screen (it goes to the huge 800x600), then I press the "option" key when y click "Scaled" and voilá! In the list of options I've found the one I needed!
Sorry, I know thi is not the post for this, but this complete the process to this P9x79 Pro install.
Thanks to all (Again)!