My general advice would be to use generic mode instead. If you can’t use the exact samplerate of the console, then it’s not “optimized mode” in the true sense anyway, and you just introduce new artefacts.
Another suggestion, looking at your last SNES image, you have quite bad crosshatching, which can be either a bad RGB cable (expecially if it’s wired sync on composite video), or you have a model of SNES motherboard (APU-01) that requires a mod to fix the crosshatching. See here: SNES diagonal lines fix
Finally, can the Elgato really passthrough to your monitor without lag? I would suggest using a splitter and send the signals to monitor and capture card separately.