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There's no one-sized-fits-all answer to this, I'm afraid. Any large-scale change to a site carries risk, and could even look like over-optimization. Even if it's a great, high-quality change, Google may re-evaluate the site, and you could easily see short-term ranking fluctuations. Long-term, you very well might improve, but there is definitely short-term risk. As Kevin said, my recent post explains the new width guidelines - it's not as simple as one number. I also don't think that falling outside of these guidelines is the kiss of death. It could impact CTR and I wouldn't make a habit of it, but some titles are just naturally longer than others. It really depends on what the before and after look like, how big your site is, how authoritative your site is, and a lot of things that are hard to dig into on a Public Q&A. Personally, I'd say test it - pick the pages where the change has the most value and the current titles are long and try changing a group of them. See how it goes. Doing it in phases and measuring can help you get a better handle on things and even help you tweak the changes as you see what works and what doesn't.