x264 video encoding...
 

First off, what's the least cpu-intensive encoding (for faster decoding, since many people have cpus that can't play back x264 smoothly) setting for x264? Using staxrip to convert.

Second, are there any convenient programs like staxrip exept 64 bit? I imagine there would be a hefty encode speed boost... obviously, said program would need quad core support.

I would say use meGUI with Shark Profiles. Either use an ipod or xbox profile for playback on slower machines.

Does staxrip allow x264 commands to be added?
I'm currently using x264.951kVAQmod.PsyRDO.core2.pf.exe from here and adding the string: -aq-mode 3 --aq-metric 4 --aq-strength 1.0
based on stuff I learned here and here.

You can also use coreavc but that cost monies. I bought a license for my brother's notebook so he could play 720p avc mkv tv rips and it works great. And the tv scene groups usually use profile 4.1/5.1.