doesn't make much of a difference (0.57s vs. 0.48s on my machine)

Agreed. But once you've reduced the time from 60 seconds to 0.6 of a second, the extra saving hardly seems worth it :) But I guess that's up to the OP.

But it does highlight the problems with modules like Statistics::Basic. It offers a OO interface, storing copies of the data internally with the intention that it only need calculate things like mean once, whilst providing access to many types of statistic which re-use that calculated value.

The problem is, calculating the mean of 7 values manually is quicker than calling a nested inherited method to retrieve it from storage. If you are processing single large datasets, amortisations can lead to savings (assuming you actually use the OO interface which the OP isn't). But for processing many small datasets, there are no amortisation gains.

The upshot is, users pay the penalties of the OO without gaining any benefits and then go off looking at complex solutions (threads in this case) to try and recover the losses.

So, 41 installed files and 3 dozen lines of code (and more), to achieve what can be done with 6 lines much more productively.