given that so many 240p signals have weird horizontal widths
Ah but this is part of the "magic" pixels are always squaire, however on output they are mashed into a 4:3 frame...
Meaning the actual pixels you see are often times NOT square at all.
Normally we think of this kind of height/width stretching as inaccurate, like displaying a 4:3 image on a 16:9 screen set to full for example.
However in the case of original content, as it was intended to be seen...
The characters on the Sony screen are too tall/thin and IT is actually inaccurate!
Too tall/thin Sony vs. Correct 4:3 aspect NEC
The pixels are being represented too closely to squaire, I will say the colors are better on the Sony.
This could be the difference in hours between the two tubes, or even wear on the caps not a true RGB vs Component color comparison...
For that you would/should be using the same tube connected both ways and compare stills, like this test I did on my old Sony 14L5 PVM.
IMO the XM29 monitor is displaying a more accurate depiction of proper pixel aspect as it would have been viewed originally.
I feel like why bother to get a display showing the scanlines if you aren't going to display the proper aspect?
Both "features" are actually functional flaws of how CRT tech works, love it or hate it these "features" are forever historically associated with these games.