after looking up "915resolution sabayon" I tried to get 1280/2 x 800/2 as extra modes for [ctrl][alt][+] under X11 for a fast magnifier effect, great for youtube videos. /etc/init.d/915resolution now exists and contains;
#!/sbin/runscript
# Copyright 1999-2006 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
# $Header: /var/cvsroot/gentoo-x86/sys-apps/915resolution/files/initd,v 1.1 2006/07/22 17:29:44 chutzpah Exp $

depend() {
before xdm
}

checkconfig() {
if [[ -z "${replace[*]}" ]]; then
eerror "You need to have at least one resolution to replace"
eerror "/etc/conf.d/915resolution"
return 1
fi

[[ "${log}" && -f "${log}" ]] && echo > "${log}"

return 0
}

start() {
checkconfig || return 1

ebegin "Patching video BIOS with new video modes."

for mode in "${replace[@]}"; do
915resolution ${mode} >> ${log:-/dev/null} || retval=$?
done
# added
915resolution 50 640 400 32
915resolution 52 640 480 32
915resolution 54 800 600 32
915resolution 58 1280 800 32
915resolution 5a 1280 800 32
#end of adds
eend ${retval}
}
#end of the file. So, I got what I wanted and 915resolution -l gives
5c 1280 768 32
as the last line, I never modified it in my changes so that's fine. You will need to list the resolutions you want in /etc/X11/xorg.conf , but I just grabbed the file [possibly whole directory] from knoppix511 which already listed them and shoved it onto my sabayon 3.26 install. One could probably also do native/4 for an x16 zoom effect but field of view problems do occur just like using binoculars or microscopes. With a good enough driver, my extra 915resolution steps might prove unneeded.