I decided to measure input delay again. This time I could use my Scart Splitter without the Sync Strike complaining (I had to use the external PSU for it) and then I could just take my iPhone's 240 fps camera and record both screens and then just take a still from that video.
The picture pretty much sums it up.
It's worth noting that the laptop I used output 1366x768 over the HDMI as it couldnt downscale 1080p onto it's own display. Therefore the HDMI view on the Amarec preview is letterboxed.
Update 8 minutes later: Thanks to Google Photos I was able to do a search for 'TV' and find this old comparison I did between my HDTV and CRT. This is a Composite source. Since 240p Test Suites measures the last digit as frames (not milliseconds like this time code video I played on Raspberry Pi), we have to convert the 70 milliseconds to frames: 4.19 frames.
Update 10 minutes after previous update: GV-USB 2. Composite Source.