I found myself the problem. Note good that if you got a gray screen, use "cpus=1" to launch the setup assistant.
However, I have another issue, that is the OS does not boot unless I boot with -x which leaves a lot of drivers/extensions not loaded.
Network for instance. I need to kextload the nforcelan before being able to talk with others.
I'm quite certain that some driver are broking the boot. How can I know which drivers are loaded or not. kextstat seems to list that, but, I have not really big differences between a kextstat after booting with -x than a boot without.