So far, I have created, using GParted live CD, three partitions, first for Sabayon, second for Windows 8, last as ext4, to be sure it is alien to Windows and won't create its default setup.
I have installed Windows 8 and it worked as expected.
I'll install Sabayon next, so I expect some trouble with dual boot (from Windows 8 part).
As note to above article, I already have a Sabayon + Windows 7 setup, since grub 1, now grub 2. I did not need EasyBCD at all.