I didn't know that about the 1st 4 cores vs the last 4. Maybe I can set those to "performance" and leave the last 4 as "conservsative". I like the idea of writing it up as a project, but I'm still developing the concept. If the point were to record video, I'd be mostly done, and in that case your suggestion to use hardware encoding is a good one. But what I really want is to try to do some real-time computer vision stuff, which needs raw frames. The purpose of doing software H.264 is really to see how much I can push the CPUs while on battery. And, I think I can push them a little further.
I didn't know about the "MFC" encoder / decoder hardware. The words "encode" and "decode" do not occur anywhere in the XU4 user manual. Neither does "MFC", but there is a word about an "XMBC". If I can get a camera to stream H.264, and then decode raw frames in hardware, then that would expand my range of choices for cameras - a lot of the "GoPrO" style outdoor cameras that have wider FOV and HDR rely on onboard H.264 encoding - you can either download the video later, or it can stream H.264, but no raw frames.
Running specific jobs on specific CPUs is good info, thanks.