There's something not ideal right now in that code, but it's a low priority item for me to look into especially as I am not too much into colors and have more important work to do, so anyone that is more concerned about colors, patches are welcome.
phoronix-test-suite/pts-core/objects/bilde_renderer/bilde_renderer.php circa line 450 with color_cache() function is where it can probably best be worked on.
I'd be curious how a system with a 64 bit kernel and 32 bit userland does in these comparisons. I've been running a system like this for years and it works great. Seems like the perfect compromise to me.
One area where I've heard people had issues was with the fglrx (ati binary) driver. It's kernel module didn't like the setup for some reason. Not sure if it was a packaging issue or a bug with the driver itself, but something to watch out for.
That's an unsupported combination because you need to build the kernel module for 64 bit and the userspace for 32 bit. Usually you need at least a 64 bit chroot to build the 64 bit kernel module in that case. That combination is only needed when you want to install/rescue a 64 bit system via chroot, there is no real good other use case for 64 bit kernel and 32 bit userspace. The things that gain speed are in the 64 bit userspace, the kernel is not that important.
The use case is getting access to more memory w/o the PAE penalty while keeping compatibility with the 32bit binary only userland apps. I thought that would be pretty obvious from the context of this article.