I'm already running El Captain on my configuration (details in profile).
No issues! I was even able to turn on default some protections:
⇢ csrutil status
System Integrity Protection status: enabled (Custom Configuration).
Configuration:
Apple Internal: disabled
Kext Signing: disabled
Filesystem Protections: enabled
Debugging Restrictions: enabled
DTrace Restrictions: enabled
NVRAM Protections: enabled
This is an unsupported configuration, likely to break in the future and leave your machine in an unknown state.
Steps to upgrade from 10.10.5 to 10.11.0 (and then 10.11.1b). I'm using Clover.
1. Download GM installer from App store
2. Launch installer, proceed with all steps.
3. Mount EFI partition, edit Clover config.plist, to RtVariables dict add:
<key>CsrActiveConfig</key>
<string>0x67</string>
4. In my case i had also to turn on Nvidia Injection in config.plist
5. Reboot machine. Boot installer from your root disk using Clover menu
6. Make a good tea.
7. Set CsrActiveConfig to 0x1 in config.plist to have most of system protection features enabled.
7. You're done!