Just making another note on a fix so that I don’t forget it.
YTG recently received a donation of about 36 Thinkpad X100E netbooks. According to my research, these netbooks were supposed to be able to play HD video, but in practice, they were stuttering even on 720p video files.
After some research, I discovered the answer. In MPC-HC, I needed to go into the options menu, select “internal filters” and uncheck “DirectShow Media”.
This more or less fixes the problem. Playback is not 100% perfect, but that might be my test files. There are still a The bottleneck (if one exists) now seems to be I/O, not CPU (CPU holds at under 20%). A vast improvement.