For completeness, I think "choppy" and tearing are quite different problems. I get choppiness, mostly - this is visible in big pans/zooms, lots of motion. It is irregular, but it looks like the image is "sticking" and then suddenly jumping to the new position in the pan/zoom without going through the intervening steps. So effectively missing frames which I know exist in the media (happens on media files, live TV, DVDs, etc). Doesn't appear to be CPU related as the CPU is very low. I have been completely unable to determine how much hardware acceleration LMCE is able to achieve out of my nVidia chipset - it should be more than capable, but just doesn't seem able to achieve it.
Tearing is more related to screen drawing, or flipping, not being sync'd with the vertical retrace of the TV, thus momentarily capturing two different images on screen at the same time, with a "tear" line being the join between them. When I turn off my vsync in nvidia-settings, I get vastly higher frame rates in glxgears (1100fps as opposed to 40fps) and the tearing starts (fairly minor), but the jerkiness/choppiness doesn't get any better! Completely stumped!