I was comparing notes with a new coworker the other week - I've got an M1 pro, he's got an M3. Running an individual test for a feature we were working on (in Rails) lines up with the 25-30% numbers quoted up thread a bit, but that's the difference between my machine taking 40sec or so vs his taking 30 or less.

It's noticeable when you've got it to compare against, and I'm looking forward to work's hardware refresh cycle bumping me to M4 next year, but I still don't think I'd upgrade if it were a personal machine (and if I can get a decent discount to buy out the depreciated M1 for personal use I'm planning on that rather than looking at anything new).