The GT 650m in VESA mode (The same mode it starts on Win without installed drivers). The OSX drivers are kicked out by the ACPI methods in the tables of bios, which can at this time not be fully blocked from loading.
To proof this, you can try my suggestion from post #192.
You should set in the org.chameleon.Boot. plist the key:
Then reboot with my DSDT.aml, which I have uploaded with removed routines for IGPU, with flags " -f -v ", placed in your Extra folder. After reaching the desktop start DSDT Editor and extract the DSDT.aml with it.
Comparing the actually extracted DSDT.aml with my DSDT. aml file, you will find the removed methods for the IGPU again.
On my Lenovo Edge I have removed the medthods for PEG0. If I boot it with in bios to internal switched graphics, they were not loaded addionally loaded.
But the SE7720 3D has in the bios no option to switch the gfx (In our case, prefered in any form to use only the PCIe gfx, the GT 650m). There is only one unified bios from Dell for the SE7720 variant with Optimus and that with 3D. Their mainboards on the hardware side must be for sure different.
On the Optimus system the gfx output of the GT 650m is send over the framebuffer of the HD4000, which is connected to the Display, to this.
On the 3D variant LVDS and the other two GFX ports are, because of Optimus can not handle stereoskopic gfx, direct connected to them.
On the windows side all bios routines are working together with the drivers. In the Win device manager, gfx part, you can not find a device related with HD4000. But the HD4000 shows up with all its methods in the on Win extracted ACPI Tables.
As I have written before in post #192, there must be a way to block the ACPI methods for the IGPU restrictively from loading and kicking out the kexts for the GT 650m on OSX.
This could work with an unlocked bios, which is save to use with the Core i7 3630qm cpu, or with a bootloader, that can retrictively block all ACPI tables of the bios and allow to load modified ones with removed methods for the device IGPU.
In my humble opinion this should be the main problem on newer laptops of all vendors, which are supporting variants for Optimus and 3D, or have no Optimus on some models without 3D and a variant with Optimus support, on the same series and only one unified bios for all models.