Credit goes to commenter Malek86 for noting that his copy of Twisted Metal Black is definitely European code, albeit outputting at 60Hz - a situation we have also confirmed with Dark Cloud.
We made an error in the original analysis below - GTA San Andreas under emulation does have some frame-pacing issues, but much of the judder we encountered is actually a result of the frame-blending, registering to our eyes (and our analysis tools) as unique frames when in fact they are simply the interpolated results of two images - we did think that it may be an artefact of the emulator working with PS2's original motion blur effect, but this is definitely not the case. UPDATE 8/12/15 4:52pm: We've been looking at more PlayStation 2 titles running under emulation on PlayStation 4, and it now seems clear that all the UK code we've tested is running at 50Hz with a crude frame-blending 'upscale' to the 60Hz output.
