Another test you might want to try is download the Big Buck Bunny AVI file and see how it plays back. Note it’s a 12Mbps MP4, so it should play easier than the Comcast recordings since you have a recent processor. There’s also a 70Mbps MPEG2 file you can download from W6RZ. Unfortunately, you need to download it in pieces and then concatenate it into one file (guess they never heard of bittorrent) but it’s a one-liner, even in Windows. This will definitely show you if you have an I/O streaming problem from your disk controller.
