I have noticed, that if you have created a project with a certain model like sonnet4, then this project has this models foodprint. It was created by and for this model.
Even if a new more powerful model arrives like Sonnet 4.5, you might experience a worse performance with this new model. I think its good for starting new projects from scratch, but not with old or ongoing projects.
So I stick with the old model as the project owner in most cases for deep logik stuff and only use opus 4.1 or so, for front end design shots.