I believe that lambda CPU goes hand in hand with memory. Your lambda@edge function will only deploy with 128mb of ram allocated and hence get very little CPU. 50ms is not low-latency in my book either. See https://serverless.zone/my-accidental-3-5x-speed-increase-of...
Good question. We just tested with ab (ApacheBench) and consistently observed the difference between Lambda enabled and disabled. We wanted to be sure this system does not incur any significant overhead and that’s why we made sure to only run the Lambda when it is needed.
We hope to see Amazon improving this, as there can be use cases for Lambda@Edge where you can’t restrict URLs so easily.