I seem to have the same problem: boot via USB, select El Capitan in Clover, Installer starts, after erasing&partitioning install starts fine. At 10/20 % of the install there is a sudden switch to a big window with one button labeled `restart`. Clicking on it leaves the system running with a gray screen. Waiting 10 minutes does not change anything both before click and after. I have checked and double checked my BIOS settings, nothing is different than the settings suggested by the OP.
Additional info:
El Capitan (10.11.6)
GA-Z170N-WIFI (BIOS version F6) + i7-6700 + 2x8GB Corsair 2133
Samsung SM951 AHCI 256 GB
Seagate 3 TB SATA
ASUS GTX950-OC-2GD5
Transcend USB3.1 32 GB
I have tried all permutations with disks, internal vs. PCIe card, and different USB ports, but nothing changed the result.
I´m quite new to all this, but isn´t there a way to switch to console at any moment and look at some logging? When I used FreeBSD this has helped me debugging several situations succesfully. Booting `verbose` sure made me remember FreeBSD
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My next step would be to vary the BIOS versions, but I don´t want to go there without confirmation that this version works.
Then I will switch to a more common USB2 stick...