etcshadow,
It appears you quoted the new guy as having said 'way more efficient', but by the rest of the post it appears you intepreted that to mean faster. Personally, I have never heard anyone say File::Slurp is faster. There are many ways to be efficient (memory, CPU, IO, run-time, programming-time, etc). While this sometimes means it results in faster run-times, it is not a requisite for it to be efficient.

Efficiency is about getting the biggest return for the smallest investment. It is also necessary to define return and investment since those are things that matter to you. Trading memory for speed wouldn't normally be said to be efficient except that usually speed matters and memory doesn't unless you run out of it.

Personally, I would have asked the new guy in what way was it more efficient. It is possible that you did ask, the response was speed, and this rant is warranted - but you failed to include that information. It is also possible that because of the file size, whatever efficiency File::Slurp offered wasn't worth the trade (programmer-time efficiency). Personally, I would like to know why it is considered more efficient as I haven't had time to look at the code myself.