I would say that you should use the latter method, the one you prefer. It is more concise, easier to read, and a little more efficient.

1% and even 5% is within the margin or error of Benchmark, so that last phrase is inaccurate.

I'm actually surprised they're the same speed. @a = sort @a; is optimized to be done in place, and I think for (@a) is optimized over the more general for (LIST) (it's definitely implemented differently).