The only way to make sure is to benchmark the different config-modules with real data and see how they compare.

Much will depend on your data: the most simple format is a "Key = Value" format, which you can simply save in a text file and "slurp" back into an array without having to use a special module.

Splitting the array-elements on \s*=\s* and saving into a hash will be very fast. But of course you can only deal with the simplest data: no embedded newlines or '=', everything ends up in one big hash, repeated keys get overwritten, no sub-key level, ...

Update: when you benchmark the different config-modules, take care that the results are not skewed due to the effect of cache-ing the file data. You may notice that the first module you test takes always longest and that repeated reading of the same file is faster thereafter. What you see is the file not being read from your hard-disk but from a buffer.

Without having tested it, I have a feeling that the major time in your config-file processing will anyhow be spent in reading the data in and that neither the config-file type nor the module used will have much effect, compared to the time needed to read the data.