I hope this might help those with remaining issues with installation of the ati-drivers package on HD5000 or newer ATI graphics hardware.
This may be specific only to my setup. I have two IPS monitors without scalar hardware. In short, each IPS monitor has a fixed resolution of 2560x1600, and only a DVI-D dual link input. Most LCDs have a scalar chip which will allow change of resolution (and actually does slow down response in games even when no up/down conversion is performed).
Installation of Sabayon 13.04 with the fixes I list in my post viewtopic.php?f=56&t=28808 almost works. Almost. I get the blinking cursor without X running even with those fixes in place.
from /boot/grub/grub.cfg seems to remove the final block of loading the ATI drivers, as the removal prevents vesafb from getting loaded in place of fglrx / ati-drivers. To make this permanent, remove those statements from /etc/default/sabayon-grub and install the kernel (and future updates) normally.video=vesafb:ywrap,mtrr:3 vga=791 gfxpayload=1024x768x16
If anyone has a different solution, I'm all ears