Switching to 256×240 optim mode does give perfect pixels as expected… but the pixels are now flickery, as if the output was jittered… which kind of makes sense, as both the NES and SNES have a video signal where every other frame have one scanline that’s shorter that’s one pixel clock shorter (340 instead of 341)
This happens with every analog source not just NES/SNES. The flickering happens because its sampling at the edge of the waveform and because the clocks are not perfect there is jitter in the waveform. So you have to change the sampling phase to sample at the center of the waveform.
You can see what I mean here: http://www.hdretrovision.com/jitter/ The sync jitter they describe there is another issue but you can see the moving waveform captures further down the page.
Check out the firmware 0.79 topic for more information about the SNES deblur. https://videogameperfection.com/forums/topic/firmware-0-79/
It is recommended to buy a 1-CHIP SNES but keep in mind that some 1-CHIPs need the brightness fix and newly found ghosting fix.