I stated what they said in two videos and on twitter.
Overall id choose the One X version for (as DF stated) almost generational better visuals with a performance mode that drops to the 50's(per what the latest video says)
Unless i watched a different video, the XSS version is near flawless 60fps, with a few dops into the high 50's, while the OneX version is almost constantly in the 50's, and drops way lower in fights.
Look its simple with OneX vs XSS. If you are happy with 30fps, go with OneX. If framerate is king and you want 60fps in most games, go with XSS.
It really is that simple.
OneX was designed to run XB1 games at a higher resolution, and the XSS was designed to run XSX games at a lower resolution.
Both machines pretty much do exactly what they were designed to do.
EDIT. Yeah just checked, its around the 8min mark. XSS basically sticks to 60fps, with the odd drop to 59fps, while the OneX is almost constantly in the 50's. Plus the OneX has texture loading problems, and although it doesnt show it here, i have seen other vids that show extra fine detail on XSS (extra rocks and rubble, bits of extra grass, etc).