I don't see how you do a fair comparison. How do you even drive a CRT with a modern graphics card? Presumably you have some sort of digital to analog converter box, but wouldn't that add a touch of latency and defeat the purpose of the CRT?
> presumably you have some sort of digital to analog converter box
Yes the CRT will display the output of that DAC in real-time. No additional buffering/latency after that conversion.
The Atari 2600 video hardware had no framebuffer and the code running on the CPU was racing the electron beam, updating the graphics mid-scanline in real-time while the electron beam was scanning that line on the display. That was about as raw and zero lag as it gets. The other 8 bit and 16 bit consoles also did not have framebuffers.
Another guy has commented here saying that in theory you could do the same with digital displays. In practice they buffer the input and add latency.