Since the 2.6.23 kernel was marked as stable under Gentoo, I wanted to upgrade to it. I wanted to stay at the 100.14.11 nvidia driver because it's the only non-beta driver at this point that doesn't suffer from this video corruption bug:
...which apparently will be fixed in 169.04. However 100.14.11 wouldn't compile under 2.6.23 apparently due to changes in the kernel ABI. I was able to make a patched ebuild using the patch here:
...and it compiled fine and has been working flawlessly since.