Behavioral engineering is way more effective than posted speed limits that often didn't seem to correlate with reality.

If you give me a five lane stroad with wide lanes and lights only every 1/4-1/2 mile, I don't care what the speed limit is, I'm doing 60+ because it feels right, and if someone does the speed limit in front of me I'll probably be annoyed.

But if I was going down the same street, doing the same thing, with the same amount of time available, but the lanes were narrowed to add protected bike lanes, the center lane was replaced with a median with trees and occasional left turn/u-turn spots, and crosswalks were added between the lights, I'm going to do around 35 because that feels right, and I won't even be mad about it. I'll just cruise down the street chilling.

Give people a street where it seems like you should be going fast and people will go fast, and get aggressive/angry when they can't. Give people a nice street to roll down and chill and that's what they'll do. It looks nicer and is more walkable/rideable too.

I mean, if you're on a bike or power walking or something I'm certain nobody's going to get too disagreeable about your speed.

This. My city keeps putting in more and more traffic cameras, but it doesn't slow cars down; it just generates revenue. If they actually wanted people to slow down, they'd reconsider having the main road look like a pin-straight four-lane highway.