yes, that's true. A problem from RetroArch cores or settings and not from the NESCE itself, it's hard to apply perfect settings, but this helped in making them more "pure".
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Hi! I've just made thinking of Master System games, as i don't have any pro controller to test other things. Anyway, slowdowns are a problem of cores, and not from settings. Maybe with Threade Video enabled, you could get some improvement but not sure if it works. I can make another zip with threade video on, if you want to try it and see if it helps.