I have a machine with very similar specification to you.
I can tell you that my broadcom 4318 is working very well with the b43 driver under Fedora 8, haven't actually tried running Sabayon on the laptop yet.
Part of the problem for some people - and I'm not saying you - is that they still try to use the bcm43xx-fwcutter program instead of the new b43-fwcutter.
That seems to require different firmware.
I got my firmware off the:http://linuxwireless.org
site, but that seems to be down this evening.