Do not use one universal CTR benchmark
Expected CTR varies by position, query intent, brand demand, device, and search appearance. Compare like with like before estimating upside.
Require meaningful impressions
A low CTR on a tiny sample is not a priority. Start with pages and queries that have enough impressions to support a practical decision.
Inspect the ranking page and query together
A title rewrite is useful only when the page satisfies the query. Mismatched intent may require content changes or a different target page.
Measure after implementation
Record the change date, compare equivalent periods, and watch clicks, impressions, position, and CTR together so ranking movement is not mistaken for snippet impact.