Noise Reduction vs. ADR: When to call it quits on post-processing?

Hey everyone,

Sofia here, location scouting as usual, but I've been thinking a lot about post-production lately, especially audio. We just wrapped a short film where we shot a few scenes in some less-than-ideal locations, think busy city streets. We tried our best with an MKH 8060 on a boom, but some of the dialogue definitely picked up more background hum than we'd like. Our sound designer has been working with noise reduction, but I know there's a fine line before it starts sounding unnatural.

My question is, what's a practical, real-world metric or sign that tells you, 'Okay, we've gone too far with noise reduction, and ADR is now the more efficient and higher-quality solution'? I'm trying to understand that threshold better from an early production standpoint to inform our location choices and on-set sound capture. When do you decide to stop trying to fix it and just re-record?