384p/400p proc name should be OK although it doesn’t indicate the fact that 360p GBI resolutions are under that group as well. As for 640×400 vs 720×400, to my understanding neither is a ‘standard’ but both are used in DOS text modes and games. Not sure if some video cards use latter’s timings for both resolutions, but I doubt there’s a single modeline/samplerate that covers all DOS 200p doublescanned or 400p modes across all systems:
I have to check if resulting pixel clock of 1600×400 mode (samplerate around 2000?) would be suitable for Line3x.