Since IO is involved, giving a damn about a few cycles of efficiency is pointless. What's more important is simplicity. Functions are entirely adequate for the job you present and can't be beaten. For a job that only a Lambda can solve, ...
Reserve lambda's for when they are clearly a good solution. They have advantages and costs that make them a very powerful tool for use in complex situations. If you can't choose between a lambda and an ordinary function, then the obvious choice is not the lambda.
