Instead of thinking in terms of "120Hz BFI", think in terms of "How can I match 60Hz CRT clarity" with emulators.
For minimizing motion blur, what you really want is a monitor with a
Motion Blur Reduction mode in your monitor. It's is often accomplished via strobe backlight. Which flashes once per refresh cycle, to eliminate motion blur.
To reduce emulator lag, you can also use RetroArch's amazing lag-reducing feature called RunAhead,
read more here. So with emulator lag problem fixed, focus on getting ULMB or a similar feature.
Now, let's focus on motion blur mathematics (1ms = 1 pixel of motion blur per 1000 pixels/second).
And 60Hz = 1/60sec = 16.7ms refresh cycle = often matches the motion blur of a common 60Hz LCD.
Without strobing, you will notice 120Hz simply halves motion blur of 60Hz.
But if you add backlight strobing above-and-beyond refresh rates, things improve much more dramatically. But good emulator strobing needs framerate = refreshrate = stroberate (aka 60Hz strobing, which many monitors do not support). The good news is most new 120Hz+ gaming monitors adds a strobe feature, so you can get 90% less motion blur...
Currently:
60fps @ 60Hz = 16.7 pixels of motion blur during 1000 pixels/second
60fps @ 120Hz = 16.7 pixels of motion blur during 1000 pixels/second
120fps @ 120Hz = 8.3 pixels of motion blur during 1000 pixels/second
60fps @ 120Hz strobed = no blur but you get a double image effect (like 30fps@60Hz CRT)
60fps @ 60Hz strobed = no blur, looks like a 60Hz CRT in motion clarity.
Software-BFI is a common workaround to convert hardware-based 120Hz strobing into 60Hz strobing, to eliminate the double-image effect. Software-BFI blacks out every other strobe flash, to give you half as many flashes, for the 60Hz strobe rate needed for good 60Hz display motion blur reduction. This is because many monitor manufacturers disallow hardware-based blur reduction at a lower refresh rate due to flicker. Because blur reduction at lower Hz flickers quite badly.
If you hate flicker, you will hate 60Hz blur reduction, but if your eyes are extremely sensitive to motion blur, and want the 60Hz CRT motion clarity experience -- then you want a monitor with
Motion Blur Reduction.
So for emulators, you have several options:
- Use 120Hz hardware strobing + software BFI. Most gaming monitors with blur reduction supports 120Hz strobing, see list
- Use the ULMB 60Hz hack. All 165Hz IPS GSYNC monitors and all 240Hz TN GSYNC monitors support the ULMB 60Hz hack. (Other models may, but it's much more hit-and-miss).
- Use the single-strobe mode of BenQ/Zowie XL2420Z, XL2411Z, XL2720Z, or XL2730 using the Blur Busters Strobe Utility. Other models only single-strobes at higher refresh rates than 60Hz.
All of them require you to purchase a monitor with a hardware-based motion blur reduction feature.
If you really hate motion blur and you don't mind flicker, then it is really worth it, here's how they compare during horizontal scrolling (platformers, etc):
ULMB (And simliar modes) has more than 90% less motion blur than ordinary 60Hz LCD.