What is the best low-lag, authentic 240p setup for SNES/Genesis on 4K TV?

[Timothy43]

I'm trying to build a reliable setup for playing original cartridge-based games from the SNES and Genesis era on a modern television, but I'm overwhelmed by the options for upscalers, line doublers, and RGB mods. I want to minimize input lag and preserve the authentic look without the blur of composite cables. For other collectors who prioritize accuracy over convenience, what's the most cost-effective signal chain you've found for getting a clean 240p signal to a 4K display? Are the popular upscaling devices worth the investment compared to a well-modded original console with SCART output, and how do you handle games that require specific peripherals like light guns that don't work on modern screens? I'm also curious about preserving save batteries.