MeGUI/x264 Settings/x264 Encoding Suggestions

General Tips

 * Don't use x264 as a replacement for a denoising filter. Make sure your input looks like what you want as output (ignoring the loss in quality from compression). Doing anything else causes x264 to run less efficiently.
 * If you aren't seeing 100% usage while encoding, remember the problem may lie with your input. Avisynth is single-threaded (usually), and so is often the bottleneck in multicore systems.

Commandline Suggestions
x264 has a lot of options, each with its own speed/quality tradeoff curve. Sometimes there is almost no reason to ever disable an option (8x8dct), other times there is almost no reason to use an option (me tesa). It's easy to build a commandline, but hard to build one that has well balanced options.

For this reason, I recommend using (at least as a base) Sharktooth's profiles. Sharktooth publishes an excellent set of MeGUI x264 profiles located here.