I read this Tim Kadlec article a while ago but the more I think about it the more I like it.
If you are going to take performance seriously (instead of just paying lip service to it or chipping away at it) set hard limits that your site will not cross. Say something like 300k total page weight, 25 requests, and 100ms response time. Nothing may exceed that. If something does, it's all-hands-on deck to fix it. Treat it like a major bug or downtime. If discussing something new that would cross the line, something else needs to be optimized or removed, or it's not added.