I personally avoid Ubuntu, so you've won my vote with #3. I propose Arch linux just as a test case... Though I think the horse has bolted on this one. Since before x64, other distro's are now doing similar optimisations, as what Arch did back in it's hey day of 686 binaries vs 386/486. I'm guessing this might be one of the reasons why FreeBSD has caught the tail of Linux, being x64 compiled with newer optimisations.
Something like this: Ask yourself what you want to use the system for. Then what you predict you will want installed.... (usually unknown) See the problem with most situations is, we keep changing our mind. So in a lot of situations we end up just starting over... I think this is where most operating systems fail though. Much like re-installing windows since it begins to crawl after a year of use... It's not logical to have a intermediate user install Gentoo and not really know what they want. Then having to start again from scratch because they mucked up a few times. Having a man page or htm readme that is a zillion pages long doesn't help either. Especially if the user just wants a fast OS that they just want to use... and install only once every blue moon.